Pull-ups for Poops

Q. My 4 yo daughter won’t poop on the potty/toilet. She uses a pull-up to poop (she is very independent in the process). She holds it if she isn’t at home. She is totally fine with peeing in the toilet and has been for about 2 years now. Two things I think are contributing are that she gets constipated and has had some pain with pooping. She says she isn’t ready to go on the toilet because she’s scared it will hurt more. We are working with her Dr. on resolving the constipation and in the last couple months it’s been a lot better. She also regressed in this area when her baby sister was born. I’m not sure if that’s still part of it or not after a year and a half. She does have a few “baby” things she still wants to do, so maybe this is one of those things too. She has said she knows she’s too big to still poop in a pull up (her dad and I have never said anything