L.,
I HAVE BEEN THERE!!!! I know exactly what you are going through. We had the same scenario with our daughter. Some things to think about...
When does she normally poop? Is it during the time she is at school? If not, then you might consider just sending her to school and then continuing to work on going on the potty at home. Being around other kids who are completely potty trained, without the pressure from you, might motivate her to start. And if she loves school, and can't attend until she has the potty training under control, that might motivate her as well.
We sent our daughter to school and I will tell you it took us a few months to get this resolved. We found the more we pushed, the more she refused. So we set a date. The three of us agreed on it. So once the date was set we were able to back off a bit. For us the date was the month her brother was to be born, and when she would be 3 1/2. We would put pullups on when she asked and then asked her to go in the bathroom to poop. That way she didn't have any extra play time while she was doing it. And it got her into the bathroom as a start. So we did that for several weeks.
Finally the day came and we did give her miralax (we had started it and then stopped it) and then we reminded her about the agreement and there were some tears, but we got her on the potty and she did it, and was so excited. And instead of us praising her, we encouraged her to praise herself (how did that make you feel, aren't you so proud of yourself...) etc.
I know when I was in the thick of it, that it never seemed like there would be a resolution to the problem, but we did it. AND SO CAN YOU! Hang in there, try not to let frustration take over. It will happen!!!