Mother in law always caused issues

We've been living with my mother in law for 6 almost 7 months, I have a son from a previous relationship he just turned 4, it gets on my last nerve that she never takes the time to under stand what he says (he has a speech problem) if you pay attention to him you'd know 100% what he says, every single day about 20 times a day she's always like "I don't know what you're saying I don't understand " she'll always ask me I never tell her cause if she ever actually payed attention she'd knew what he said, she'll even complain to her family she never knows what he Is saying. I swear I can't wait to leave, my husband can come visit her when we move but I ain't ever coming back.