Oh yes, I know your situation well
DD1 is 4.6 and out of nappies since 2.4
Since then have had several episodes of regression (weeing)
NOt quite the battleground you describe in your OP, but lots of not bothering to go and not caring she's wet etc
Each episode lasts a couple of weeks and will involve a few accidents a day
I can categorically state that for DD nagging her, reminding her, star charts, treats, bribes, toy-removal, getting cross, praising for going/not wetting etc etc DO NOT WORK
The only thing that improves it is to COMPLETELY IGNORE it
So an accident gets greeted with an "Ok, go and get changed, then". And THAT'S IT
She's been dry for ages now (has the odd accident, but hey, she's 4) I suspect that age has improved it. She realises tht toiletting is part of the daily routine you go through... a year ago she just saw it as a hassle, a lot of the time
And in the grand scheme of things, It's not that serious, is it?
Good luck, I do know how frustrating it can be