She's a white-tailed deer hybrid. 

She has an adorable nose :D

She has dark brown, short-furred deer legs. They help her jump and run better. She can jump at a minimum of 4 blocks and can run .5x faster than the other hermits. But her legs aren't very good for swimming, so she drowns a lot.

She gets scared by the littlest sounds and 8 out of 10 times she runs very far away and the hermits closest to her need to look for her. 

X (with her permission) put a tracker in a watch for gem so they can find her easier.

She for some reason has antlers? I'm not quite she what headcanon I could have for that.. maybe she had a genetic mutation and gained a male deer gene. I'm not sure.

She has a special connection with birch trees as she was born in a birch forest and only knew birch trees for most of her life.

She has powers similar to a faes' (Plants). She can grow flowers but she can't really control it. The last thing is that her mood affects the flowers and rarely the trees and seasons. If she's feeling down the flowers will wilt and turn a darker color. When she's happy the flowers will sorta glow in the vicinity. 

Gem is kinda like the groundhog on groundhogs day, but she is 100% honest on if it's going to be spring early or not.