My 3.5 year old was doing the same thing. Waiting until the end of the night to poop in his pull-up. I would notice him walking on his toes and clenching like he had to go really bad. He would bring me the pull-up and cry for me to put it on him. When I put him on the toilet he would cry so bad and I would have to hold him there until he just couldn't hold it anymore. After maybe 3 times of this happening he seems to have adjusted to it. Now he'll say he has to "doodie" and seems much more chill about it. I did a lot of celebrating when he went, let him look at it in the toilet and let him flush it.
I read "oh crap potty training" and that book really helped me with ideas and strategies and problem solving tips. In the end I used small treats to get things going when my son didn't want to poop and after about 3 days I fazed the treats out.
Try putting her in the potty before you put her pull up on before bedtime and use training underwear during the day. It also helps if you go poop with her, so she feels confident about using the potty for poop. My son was the same way but he would hide when he pooped. So I started to show him that i went poop in the toilet and not in the undies. He finally got it down a week later and his fear of poop went away.
Following my daughter still pees and poops in her diaper and occasionally will use the potty to pee only. I tried giving her undies, let her pick them out and everything.. she kept asking for her diaper back.