(Trying to go for some different Prefixes here, so if the prefixes seem odd thats why)

I will keep this in mind, as long as you can justify the names I most likely won't knock it down for being odd. 

Name: Joyheart 

Ah, I see what you mean. Usually, I'm not into the idea of having an emotion as a prefix. It makes zero to no sense as this is a name given to a kit who had recently been born, not a full grown cat who's personality is evident. That being said, I won't knock it down until I've seen the reasoning, this is just my first impression of it.

Prefix: Joy because she has a orange stripe on her face that makes it look like shes eternally smiling.

Interesting. Still, I would maybe stay away from Joy even in this case. Maybe having -grin as a suffix could make up for Joy. The only reason I can see Joy being a reasonable prefix would be if the cat had previously been a rouge or kittypet. Kind of like how Billystorm got his name.

Suffix: She's loyal and very 'by the book' as it horrifies her to break the code / lie. 

That's completely reasonable! Nice job. Overall, I would change the name a little just to make her seem not too out of place. Maybe Lightheart or something along those lines? Light being a replacement for the light and happy feeling you get when you are filled with Joy. Of course, this is just my recommendation and you don't need to take it. I think its interesting you're purposely choosing odd names and I don't mind this one too much c:

Gender: She-cat

Can't exactly rate this, but cool, she-cat. ╰(✧∇✧╰)

Age: 58 moons (4 yrs, 10 months)

  Yay! I'm quite tired of seeing 20 moon she-cats. It's just too common, I'm glad I get to see an older she-cat.

Clan: ForestClan (Has the attitude of ShadowClan, abilities of SkyClan, and lives in high mountains full of evergreen trees) 

Interesting. But the name is common. Maybe something like GladeClan, GroveClan or TimberClan? Just a little bit of creativity. Forest just sounds a bit too plain to me.

Status: Senior Warrior

As said before, love the idea that she isn't just some newly made warrior.

Apprentice(s): Emeraldshine (russian blue she-cat, bright green eyes) , Brasspaw (Tawny Tom, white around eyes and underbelly with hazel eyes) 

Not bad when it comes to names. I'm not big when it comes to metal/gem names, but I am a fan of Emeraldshine. Brasspaw is still "meh" to me, but I'm sure I'll warm up to the name.

Looks: Shes a Maine Coon cat, so she's big, fluffy, bulky, and has big paws. She's a light brown torbie, with flecks of brown, black and orange throughout her pelt, but her main color is light brown. She has black tufts on her ears and white tufts on the bottom of her feet. She has a white muzzle, white feet and underbelly. her tail; which has flecks of grey, resembles a squirrels tail in terms of fluffiness. She has yellow-green eyes. 

Overall, very realistic. Fluffy she-cats are very common in the fandom, but this one I don't mind at all. Also, I love seeing she-cats with yellowish eyes, usually everyone gives their OCs blue or bright green eyes. 

Personality: unlike her pretty outside, She's abrasive and opinionated. She is not afraid to be brutally honest. She's passionate in everything she does, and is not afraid to publicly announce why. If you insult anyone she cares about, be ready to lose some fur. She's proud, confident and competitive, and she knows her strengths and her weaknesses. She's ambitious, but shes smart as well. She stands by the warrior code and nothing else; and would never betray her clan. 

She seems to have her fair share of pros and cons, so that's great! I feel like she would be an apprentice who would get in trouble a lot for her confident attitude and attacking those who insult her friends. She seems well-developed and a cat I could picture in the canon series.

Scars: Nothing serious really. A chip in the ear and some scars from former battles.

Simple scaring. Nice.

Likes: defending her opinion in strong verbal fights, then winning over other cats because of the facts she gives. She loves a good Hunt, and a good, fair fight. She likes teaching apprentices how to be strong and confident in themselves by giving them praise and telling them to never stray from the code. She also likes quality time with her friends and family, and once in awhile, doesn't mind a good story from the elders or playing with her siblings like a kit. 

  I get Hollyleaf vibes from her for some reason. Sort of like a more accepting version of her. Overall, such a sweet heart! I'd love to see her develop some hobbies for herself.

Dislikes: She hates the warriors who think little of their apprentices and don't give them the time of day they need to succeed to their full potential. She also hates cats who express woe and sadness over petty things. She hates all the lazy cats who don't help make their clan as strong as it can. She also hates swimming, and fishing. She doesn't like hunting birds either, as they are too fast and high for her build that makes her a poor climber because of her big size. 

I'd like to see her hate more small things, maybe even a fear. Something small like being scared of spiders or maybe she has a hidden fear of water but doesn't let anyone know since she doesn't want to be looked down on.

Kin: Spottedflower (Mother - Elder - 81 moons) A white Maine Coon she cat with brown, black and tawny spots. Green eyes. 

Interesting, no real complaints on her. 

Burningclaw (Father - Senior Warrior - 79 moons) An elderly dark ginger tabby with yellow eyes. He's getting a little old, but doesn't feel like joining the elders just yet.

  Nice! He's still young to consider the elders den. If he's in good shape, he should be okay for a few more moons. I'd say around 85-90 moons is when he should fully consider it. 

Pumpkinseed (Brother - Medicine Cat - 58 moons) Dark ginger tabby with a white underbelly, toes and muzzle. He has green eyes. 

Oh my goodness I love the prefix Pumpkin! It's one of my favorites, but I don't use it often since I already have a kittypet OC named Plumpkin. What a cutie!

Heartfeather (Sister - Senior Warrior - 58 moons) light brown with black legs, a black tail tip and black ears. she has a black splotch on her chest that almost looks like a heart. Yellow eyes.

I really dislike Heart as a prefix, it just seems odd to me. That's just my opinion.

Dapplekit (Sister - IchorClan spirit - death at 4 moons) And exact replica of her mother; white with brown, black and tawny splotches. (IchorClan is kind of like the Dark Forest) 

Dark Forest for a kit? That seems like a bit much. I can't think of a reason a kit would go there instead of StarClan.

Mate: Icepelt (Mate - Senior Warrior - 60 moons) pure white tom, long legs, and is overall lean. Great fighter, but is calm and reserved. He keeps Joyheart from creating TOO big of a scene. Has bright amber eyes.

Nice! He seems like a perfect match for Joyheart's personality.

Kits: Blazefoot - (Son - Young Warrior - 17 moons) fluffy dark ginger tabby on his upper body, such as most of his face, ears, back and tail, but his lower body is all white, such as his legs, underbelly, chest and around his muzzle. bright amber eyes.

Blazefoot is a bit too common. Maybe Blazestep or Burntfoot?

Featherfall - (Daughter - Young Warrior - 17 moons) a fluffy, long legged dilute calico cat, with faded fawn, grey and fading tawny. green eyes.

Same as before, Featherfall is rather common. Maybe Featherglide or Featherdrop?

Littlekit (Son - IchorClan spirit - death as newborn) a fluffy, white kit with brown splotches. He used to be a SunClan cat, but he followed Dapplekit around, eventually getting lost with her in IchorClan territory, not ever finding his way back to SunClan.(SunClan and MoonClan is like StarClan, but you go to MoonClan if you die in the night, and SunClan during the day.)

  Once again, Dark Forest is somewhere that evil cats go, not newborn kits. They wouldn't have time to develop into a terrible cat.

Skills/Flaws: She's good at hunting rats and mice; Maine Coons are naturally good mousers, and because of her big, bulky size, she's good at fighting too. She can survive a snow storm, which happens where they live, because of her thick pelt. However, she cannot climb trees well, because of her size, small branches can easily snap under her weight, making climbing not very safe to do. Because of this she can't hunt birds well. She isn't very speedy, either. She doesn't like swimming, because dragging her heavy, wet fur around is not fun. Fishing for the same reasons, plus thats not what her clan hunts.

Understandable and realistic. c:

Backstory: Don't wanna spoil the book about her, its not close to finished, but I don't want to spoil the plot. Story is called "Joyheart's Fall"

Don't worry, I understand c:

Extra:Dapplekit went to IchorClan because she was so jealous of her siblings because they got a future, and she manipulates Heartfeather that the Clan that took her and killed her; RoughClan, deserves to die. However, Heartfeather is too nice to do anything unless the leader tells her to do it. Dapplekit also has turned Littlekit into a manipulative spirit, and Littlekit haunts Joyheart, Icepelt, Blazenose and Featherfall.

Again, kits are too young to become this wicked. Young minds are much more open and accepting, even if they are vengeful that's not enough to send them to such a place. You go to the Dark Forest because of your actions, not because you're jealous. Maybe you can justify it a bit more?

9/10 - There are still some things that don't make sense with her, but can be patched up with some effort. Overall, she was a lovely character to look over.