I want to ignore my mother in law.
Why do you want to ignore her?
She constantly reminds me of my shortcomings.
I'm sure that it's frustrating having her do that, but you shouldn't just ignore her since that won't help things. You should consider telling her how you feel so that maybe she will change her behavior toward you.
I'm done being nice. She's always on my ass and making me feel bad.
I understand that you feel angry and upset about how she is treating you, but treating her the same way will just make things worse. Tell your partner how you feel and maybe the two of you can talk to your mother in law together. That way your relationship can improve.