Hello. I have a 4 year old niece who when looks straight up one of her eyes turns left or right I can't remember.

She is too young to tell us what she is seeing but she is not clumsy or anything, I play with her with staffs(martial arts sticks) alot where I slowly go as if I'm going to hit her over the head and she blocks it alright.

I was wondering what this condition is called and what steps could be taken to 'fix' her eyes. I used to have terrible nearsightedness but I refused to wear glasses and instead I focused* intentively on using my eyes and a few months later my vision was fixed.

I am aware that most problems like atrophy in muscles or eyes and such occur because humans stop 'using' their body. My niece's problem is different than nearsightedness obviously, but what can I do to help her fix this problem?