Contact your lawyer(s) to get their opinion on the situation, and do not talk to her in the mean time. If they say she has no case and for you to leave it be, leave it be, if they say she has a feasible fight against you, then get ready to see the court room. Just make sure that everyone who was there is willing to participate on your side and not hide on the sidelines. The more witnesses on your side the better. Also, don't say anything to anyone (aside from your lawyers), that may incriminate you. If a police report is filed, don't tell them anything they don't ask, but if they ask, tell them everything you know/remember. In order, and if you could even get it in writing and get a few copies of it, one as a hard copy, and one with the signatures of everyone who was there to back your side of the story that would be best, epically if this does happen to go to court.
EDIT - Also, because of my accident I had in November, I always carry a camera in my truck (digital, disposable, or whatever), just for situations like this, take before pictures, and pictures of every step you had to take. Make sure the license plate is visible in the pictures, and take one of the plate of each vehicle, making sure there is a picture of the entire vehicle in the initial position. Cover your ass by taking as many photos as possible, Photos don't lie, people do.