A.W.
It'll just take time. When she does poop in her undies, change her in the bathroom and dump the poop in the potty so she can see where it goes and let her flush it down. She is already doing so well, I'm sure it'll just be another month or so and she'll be all done. Track her and see does she poop at about the same time everyday? If so, read her books on the potty during that time.