She criticizes your pie, raises children and hints that her son could do better. Sound familiar?
A war with your mother-in-law is a losing proposition. But you can make her… your friend.
The first step is to stop seeing her as an enemy.

Understand that her behavior is often dictated by the fear of losing contact with her son. Instead of arguing, ask questions: "Why do you think he did this?" This will move the dialogue into a peaceful direction.
Step two - find common ground. Even if you hate embroidery and she loves it - ask her to teach you.
Let it be your "secret". Or give her flowers for no reason - this way you will take the place of "caring daughter-in-law" in her heart.
Step three is to set boundaries gently. If she arrives unannounced, say, "We're so happy to see you!
Next time, let me know so I can bake your favorite pie." This will make it clear that it is better to coordinate visits.
After six months of such maneuvers, you will notice that her comments have become less frequent, and she praises the pies.