What is between being walked on and standing your ground.

My mother in law is coming to stay with us at the end of the month for my daughters first bday. We’ve had some very bad experiences in the past so I’m trying to do the work to get myself in the right mindframe so I can at least act in a way I am proud of.
When she first came to visit my daughter at 2 weeks old I let her walk all over me. I had just been through a lot with giving birth and didn’t feel I could handle confrontation. I let her do whatever she wanted with my baby even when it made me very uncomfortable and went against my intuition. I felt like I let my daughter down.
We went on a trip together when my daughter was six months old. I felt so pumped up on scholars and knew this time would go better. I told her no when I needed to and every time it seemed to make her more and more and she would just treat me worse and worse… I know that’s a judgment. I eventually shut down. I just decided I would just get through it.

I want this time to be different. I know I can’t control her behavior. On the boundaries podcast it sounds like setting clear boundaries are the answer to what’s between being walked on and standing up ground. But what boundary can I set for someone who is staying with me for a week and just constantly saying “mean” things and telling me how I’m doing everything wrong when it comes to being a mom. That’s up for interpretation so it’s hard to set a clear boundary. I am scared that I am going to shut down again but this time I can’t bc I need to have it in me to throw a party for my daughter. I am trying to incision myself handling every comment she makes with grace. But after the 50th one it seems to get to me even when I’m using all my SCS tools. Thanks!