My friend's mother is dumb and deaf. She prays Nimaz regularly in her own way, but she is not aware about pure and impure, or the correct number of units. Should we let her do what she is doing?
If she is able to understand and rectify her mistakes in the acts of worship, then you should politely tell her and help her to perform acts of Wudhu and Namaz properly. But if she is unable to understand or unable to perform properly, then she is not responsible for more than what she can.
Wassalam.