This may not help much, but I'd just let it go for now. My oldest son was very stubborn and hard to potty train. He was pushing 4 before he was trained during the day and 4 before he was a night. Because of the headaches I'd had dealing with it from the point he was 18 months old, I guess I was in denial about having to train my second. I never made an issue out of it. If he asked, we went, but it wasn't often. I figured he'd be a nightmare too. However, 1 month after he turned 3, he told me he needed to go potty, so we went. Well, from that moment on, he never had an accident, day or night. I didn't do anything. No bribes, no nothing. It was totally on his own. To me, if you wait until they are ready and don't make it a struggle, it is completely simple. Sounds to me, like she's in a power struggle with you over it. Even if you do make any headway, she'll probably regress when the baby does. If I were in your shoes, I'd wait until after the baby comes and try again as she has gotten used to being the big girl.
Also, just my two cents, I don't believe kids are truely potty trained until they stay dry on their own intiative and go to the bathroom without urging from you (aside from, it's time for bed, let's try and go potty). Kids that are "potty trained" as such young age, is more like the mom is potty trained and taking them potty every half hour. It's the mom's intiative, not the kids. Kind of like people saying their 12 month old knows the alphabet when they are really just singing a song as they would "Itsy Bitsy Spider." They don't really have an understanding of what it means. (I hope that makes sense)