my MIL has started squeezing out my newborn's nipples, saying it is important to release any milk or residue. i can't see my baby crying in pain. is this really necessary or should i make it stop right away?

I gave seen people doing this but I came to know about this only later when my daughter had passed that age when that is supposed to be done. Well! I do not think that is important as kids who do not go through this grow up to be fine. Also her PD never mentioned this to be done. If it was really important, doctors would have mentioned this. If you believe in it then let her squeeze that milk out it wouldn't harm the baby either way. Else best is ask the PD.