My OC Isa can change her appearance at will, as long as she turns into someone humanoid, as well as summoning wings occasionally, but she gets exhausted easily.

Would it make her OP/godmodded/Mary Sue if she can change her outfit at will too?

Or if I give her a form that looks like someone from Sonic, but she can't really do anything?

What about a form that allows her to temporarily breath under the water?