J.N.
It could be one of two things.
First possibility - she doesn't know how to control it yet. Knowing that she has pooped or peed doesn't mean that her body has developed the ability to know she needs to, or maybe the control to get to the potty on time (although, if she runs into the corner, it's less likely, see the next)
Second possibility - it's become a power struggle. Did this with my son for way too long. Finally (when he was almost 4) I gave up and put him back in diapers. I also told him that Nintendo (something he liked to do) was for big boys who went potty. I didn't bug him about going potty after that, but when he asked for Nintendo, I reminded him it was a big boy thing and big boys went potty. It took a few months (part of which he decided he "didn't like Nintendo anyway") and then he was ready (it helped that his big sister still got to play) and was 100% trained in a week.
Either way, you may just want to wait it out. And diapers cost less than pull-ups, so stay with them until she's really ready to go!