Toddler won’t poop

My toddler will be 3 in June. She is 100% pee trained throughout the day/night but will not poop in the potty. She will poop in her underwear THEN tell me she pooped instead of going to the potty. She’s not enrolled in preschool/daycare but she watches us go all the time. What makes it worse is my mom is saying my parenting skills are bad because she should have already been potty trained at 1.5 or 2 yo. I know I have to be patient but my mom doesn’t understand. She wears underwear during day and pull up at night so she doesn’t poop in the bed. suggestions please?