My DS1 just told me one day (just 2), he didn't want nappies. I had just had DS2 so wasn't keen. I told him fine but he'd have to go in nappies if he had an accident. He never did. Not even once. Week after he said the same about nights. Same happened.
DS2 is 3.5. He wasn't interested in using the toilet. Rewards didn't work. He gave anything to DD or DS1 or just said outright he didn't care about stickers/ treats etc. Then one day I said he could watch an episode of Go Jetters if he went dry (screen time is usually once a week after swimming). That was it. No accidents. He still has a nappy at night for now.
I suppose my point is, they'll do it when they want. Listen to what they say find incentives they will really want. Both mine skipped the potty and went straight for the toilet. Both really different personalities.
We've never had an accident in the car and I think it's becasue the expectation is they will be dry / we trust them (nerve racking on the first few trips!) So they are. But by their choice.
I would say on both occasions them seeing a younger sibling in nappies spurred them on to be dry. I think if you rush it you'll be in for lots of accidents. We used pull ups for DS2 when he started nursery, I personally think that was a mistake for him.
Every child is different so do what your gut tells you. If I were you, I'd just ask her what she wants and follow her lead. I've seen my friends struggle with endless changes of clothes etc. Which I do think is down to the parent choosing when the child will be dry, rather than the child saying.
Thank goodness I only have to do it obe more time lol. Good luck :)