Take photographs of damage to your car.
If she reversed into you, the damage will be a dent to the area of impact. If you were performing an illegal manoevre and she was stationary, I find it hard to see how you could have moved side on into the rear of her car - if this was the case, the damage would be scraping damage rather than a blunt impact type dent. Take photos of your car (her car if poss), the scene. Draw a diagram and write an extremely detailed statement immediately - take measurements too if you can.
If this goes to court (and on what you have said, I would not admit liability) cases are won and lost on the evidence. you will need more than your recollection (which will be dimmed after time). If you are the claimant, you have the burden of proof and so you need to make sure you can discharge that burden.