wont poop on potty

[galesville1980]

My DD turned two in march..she is doing great peeing on the potty..she will say she has to poop and will sit on potty to try but wont..then i put underwear on and with in 2 min she will poop.....my DS was fully PT at 2 so never had to deal with this b4...need tips on how to get her to poop on potty.