M.G.
See to me, if she started having accidents after a month then she wasn't fully potty trained. At 2 1/2, it's rare for a child to be fully trained.
To me, when a child can hold it all the time, doesn't need to be reminded except for say, before long car trips or going out - then they are potty trained.
I think what happened in your case is you've made far too big a deal about it and it's become a 'thing'. All this taking her to the doctor and having her tested, and her getting angry at herself - what a lot for a 4 year old.
I think you might be stressing her out. I gave one M&M for the first few days - that's it. A big hurrah! the first few times. Prizes to dates with dad? C'mon. You are making this a HUGE deal.
If you back off - no mention of it, just deal with accidents calmly and just let it go - and no more rewards, attention (negative or positive), just say - "We're going to let this go for a few months, ok? When you're ready, it will all happen just as it should." Then let it go - I think you will find things just progress better.