I mean at best for Derpy we know these facts-
She doesn’t speak often
She has a lazy eye
She’s clumsy
If anything you can say maybe she’s a selective mute with strabismus and poor depth perception.
The rest is just pure speculation without evidence.
It’s worse when they decide on a personality for her. If you run an ask blog and she doesn’t meet their very specific idea of how she acts, then you will receive HATE! On MASS! It’s crazy.
Top that off with every Doctor Whooves blog being targeted if they don’t have Derpy.
My headcanon is that her eyes are like that because she looked into the heart of the TARDIS which also made her a supergenious (Because she saw the whole of time and space) but it’s only in spurts of genius. other than that, she’s pretty normal, other than her eyes messing with her coordination.