We had something similar and now it is a distant memory but I remember how maddening it was.
It sounds like you think she might be being awkward - this isn't how I saw it with my DD. She was nearly 3 when we started - did all the preparation/ build up - big girl's pants, no more nappies, lots of potty-themed books to look at, seeing friends of same age use potties etc etc and DD was really up for it. But she too just could not let go - she would be skipping from one leg to the other saying "I'm alright, I'm alright, I'm alright" when she clearly wasn't. This could go on for over an hour if I was with her all the time - it felt painful to see, like a difficult labour! Then, as soon as I went upstairs to get a book etc, she could finally let go and there would be a flood. I knew she couldn't help it as she was so keen to please; she's quite an anxious child and I genuinely think she was so keyed up about the whole thing, and trying to do it in the right place so as to get her blessed sticker, she couldn't relax the sphincter. I kind of know how she felt - I can never wee in the sea, no matter how desperate i am!
How long have you been trying this? We kept it going for 3 weeks in the summer (really needed to be able to stay in the garden), with her holding it in all day at nursery as well before a big flood on the floor, until I got concerned about the effect on her body. So, we went to see the HV, DD listened intently to the whole conversation and HV and I basically decided we needed to go back to nappies for a few weeks. ONE HOUR LATER, back at home, lo and behold, DD's first ever wee in the potty. I still can't quite belive it, but from then on, sticker charts a-go-go and mad amounts of praise later for every success, she is totally there. We still get called in to see every poo and wee. But now she really wants to go nappy-free at night-time, hence I'm back here looking for tips! I also can't get her off the potty and onto the loo, but at least she's not wetting herself.
Good luck - it kind of takes over your life for a bit doesn't it.