I highly recommend the book "Toilet Training in Less Than a Day". I saw it recommended on here, bought it on Amazon for I think about $6. I bought it because I figured even if I got some ideas that made it less stressful, it was well worth $6. Well... my son potty trained in a day! It was one of the least stressfull things I have had to do with him.
The advice I would give that I beleive was the most help was:
1. Put them in underwear and keep them in underwear. If they have an accident, let them change themselves. They will learn a LOT faster that way. Also, teach her to do everything completely on her own. Everything from pulling down her pants, wiping, pulling up pants and underwear, and even emptying the potty chair and flushing... they have less accidents if they are relying on themselves, instead of waiting for you. Teach her to just go in and go without needing permission when she has to go. Independance is a huge part of this. I know a lot of people don't want to let their kids make a mess... but they can do a lot more thtemselves than they get credit for, and it is easier to clean up after them the first few times, than have them dependant on having you clean up after them every time.
2. To get her to have to go, get her to drink as much as possible of whatever she will drink. She will be constantly going, and will learn fast that it is uncomfortable to be wet.
3. Plan to stay at home for at least a couple days, and let her focus on going potty. If she seems ready, take her somewhere the 2nd day (we ended up spending the whole 2nd day out... when I had 3 days off work to stay home and potty train, for a total of 5 days. I really only needed 1 day!)
4. The book explains how to use a doll that goes potty to motivate and teach her.
5. Most important (along with the underwear, NO pull-ups!), is to be positive and reward her. The book recommended salty treats, instead of sugar, because they make you drink more. I got chili frito's (usually my son doesn't get junk food or pop... for this he did! It's only 1 day, and makes it exciting for them). I would check every couple minutes, if he was dry he got one frito. If he was wet he didn't get any. If he went potty on the toilet and was wet, he got one, and if he was dry when he went, he got a whole handful. I kept reminding him how happy everyone would be, listing off everyone he cares about, and how happy it would make them that he could wear big boy underwear. I also kept reminding him how happy it made mommy, and he really focused on that. Not one negative word. Just rewards and inspiration.
His first day... I was thinking he might not be ready. He was constantly having accidents, and I didn't think he would make it. The next morning he woke up and stayed dry the whole day. We never went back. If you are nervous about underwear in the car... take a plastic bag (like a Cub or Target bag) and put it on the bottom of the carseat. The seat will stay clean, and she will still learn. He had one time that he had an accident on purpose when he was mad at me... in a grocery store when he was tired and crabby. I told him I couldn't hold him because he was wet and it was icky, and made him sit in it until we got home (I had extra clothes, but I wanted him to learn from it). He has never done that again.
Good luck!
J.