Can we also claim a disabled tax credit?

There is no such deduction as a disabled tax credit. You are claiming her as a dependent. In order to claim her medical expenses, they must be greater than 10% of AGI.

There is no specific "disabled tax credit". You MAY be able to qualify for Dependent Care Credit depending upon your income level to pay for supervision and care while you or your spouse works/goes to school. There are conditions to that. There is an additional personal exemption amount for filers over 65 and/or statutorily blind. Really, you can only claim her medical and care expenses associated with that IF YOU ITEMIZE. Most people just get to claim that person's personal exemption and that is it.

I did taxes for a while. Dont know what disabled tax credit is but if your income is low you can claim a disabled sibling that lives with you on Earned Income Credit...I know cause I did.

You can claim as a dependent anyone for whom you provide more than 50% of support.

See a tax prep company. I know of no such thing as a deduction for a mental impairment.