Mother in law is driving me crazy

So my DH's little sister has Down syndrome. But it's a very very acute Down syndrome. The doctor literally told my MIL that it's really only enough to make her look different. The thing is my MIL treats her like she can't do anything and it aggravates me to no end. She's not aloud to pick out her clothes, she's not aloud to tie her own shoes, she's not aloud to give herself a bath. Might I add that she is 11 years old... Another thing that aggravates me is that she practically does her homework for her. Gives her all the answers instead of letting her try to figure it out. How will she ever learn anything?