One of our FDs was defecating when she was angry. We offered ballet lessons for when she was "potty trained." Yes, we knew it was on purpose but we treated it like a potty training thing. We clapped when she pooped on the toilet and reinforced her good behavior. Now she is in ballet classes (they both are) and it's a non-issue.
I agree with this. Treated it like she is doing something bad will just give her reason to keep it up. Act like it is a potty training issue. I would even stick her in a diaper for 24 hours after an incident. (Not the same diaper- but you know what I mean.) A lot of potty trained 3 year olds would not like being in a diaper. But if she can't control her pees, then she must need it, right?
Just stay calm and don't feed into it. It's like walking away from a tantrum. You don't want to acknowledge it AT ALL or she will continue.
Offer a big reward for being completely potty trained. A trip to an amusement park or a new toy that she wants or classes of her choosing.