Mom overfed my daughter?

Josephina
Is this something that older parents just do? I don't understand. My daughter is six months old, she suffers from MSPI and GURD. This conditions led her to be diagnosed with failure to thrive. Her regular doctor and GI doctor have told me that she is not failure to thrive because I'm not feeding her, her other two conditions are the cause. My daughter has a scope surgery scheduled next week, to get to the bottom of the problem to see why she can't gain weight fast enough. My mom is really on edge about this. She firmly believes that I don't feed my child at all, even though she goes to all doctor appointments where she is reassured that it is nothing that I am doing. I live with my mom and she sees me daily feeding my child, I also fill out a white board feeding chart so she knows exactly when my daughter eats. My daughters doctor said NEVER try and give her more milk that she usually takes, because she often aspirates while eating, and has projectile vomit after feeding. Well, yesterday my mom watched my daughter while I went grocery shopping. My daughter was acting really uncomfortable and kept projectile vomiting, and crying. My mom fed her NINE OUNCES OF MILK. My daughters maximum is FIVE. I confronted her and told her she cannot do that. And she claims that my daughter is "starving" and I would feed her 9-10 ounces she wouldn't be FTT. That is not true, as her doctors have told us many times. Overfeeding her makes it worse. Idk what to do about my mom. My younger sister was also FTT due to extreme allergies, so my mom should know better. How do I get her to stop this harassment?