V.W.
I had a friend who's 4 yr old son did that. At 4 he still refused to go except in a diaper. Don't make it into a power struggle. I would suggest offering a reward for going poop in the potty. Don't punish if she doesn't do it, but if she DOES, then let her choose from a bag of treats. I used a ziploc baggie filled with colorful individually wrapped lifesavers for my son... it worked great.. there were so many colors it was very enticing and it was in his control to choose. They are only like 4 calories each, or something, so even if he got 4 a day it was no big deal (junk food wise)... gradually.. after going on the potty became habit, he forgot all about the candies....
If lifesavers aren't her thing, try something else... get a bag of M&M's and let her pick 2 each time she does it. Or whatever treat you decide... I would just try to make them colorful so she gets to "choose" something.. not just get "one more of same old same old"... have fun!