Oh my dear, dear, diva.
This is one topic on which I have LOTS to say. Let me give you the background. I have three children. My oldest (son) has Downs syndrome and my next child (daughter) is 20 months younger than her brother. I picked them up at day care one day and my daughter said she no longer wanted to wear diapers. A few older girls in her class were training and she wanted to try it. She was just over 2 at the time, that meant that oldest son was nearing 4 (and not yet trained- not even begun!) So we tried it. Things were going pretty well for both of them. My daughters reward was a handful of M&M's (sitting in a big see-through jar on the bathroom counter). My sons reward was McDonald's french fries. Not easy to put in a see-through jar. So I went to Micky Dee's, explained the situation and they gave me some empty ff containers. I made a huge poster with these containers stuck to it (think 3-d) and then stuck the poster to the wall in the bathroom. Each time they "went" or sat on the toilet I had to sing "Take Me Out To the Ballgame" for son and "The Barney Theme Song" for daughter. And I forgot to mention one thing. We were building our own house at the time, 2 miles down the road. I mean... we were building it ourselves as in the creating the drawings, clearing the lot, using a backhoe, laying the foundation brick by massive brick, framing, the whole shebang. I was a crazy woman. My life consisted of going to work, coming home to sing Barney in the bathroom, and then going to the site to do cleanup after hubby had been there every evening working. I finally relented to driving our minivan because I realized that I could fit a potty (with the cup lined with a trash bag) in the back and it could be a make-shift bathroom. It was all very sanitary. Lots of wipes on hand, more trash bags, we never ever made a mess or had an accident.
About 4 months later, they were both trained. 5 months after that we moved in. 12 months after that son #3 came along. 2 1/2 years later I decided I've had enough of diapers and start to train son #3. I read him his favorite book each time he went in the bathroom (Are You My Mother by Dr. Seuss, I know it by heart now). He was passive agressive, and absolutely would not use the potty. No amount of bribes would work, and let me tell you we eventually bribed him with everything. The ultimate bribe? A trip to Disneyworld. No kidding. Still wouldn't use the potty. He would have an accident and not even acknowledge it happened. I knew he understood the entire process, and he knew I was frustrated. Finally, one day, a year later, yes that's a year of this, he tells me he has to poop. I take him to the potty, HE POOPS. I'm screaming out the bathroom window to the entire neighborhood. He hops off and says "Can we go to Disneyworld now?"
Never an accident or refusal from that day forward. And of course, we went to Disneyworld almost immediately.
The moral of the story, my dear, dear Diva Severine: you need to let her be in control. Your daughter will do it when she's ready. Forcing her or being firmer will not help the situation, and will only prolong the agony for you. I know, I know, it's very frustrating for you. But if you let her be in control she will do it when she's ready and it will be sooner rather than later. Have no reaction at all when she has an accident, and praise her when she uses the toilet properly. She sounds very smart! If I had to do it all over again with #3, I would have sent the white flag up and just surrendered to him. I hope you will do the same. Try it. I know you'll get results. I have many, many friends that were in the same boat I was in at the time. The kids were all the same- refusal, wanted to be in control. I speak from experience.
Good luck, and PM me any time you need to vent or share. I am here for you!! I've been there!! Hang in there! I'll be thinking of you.