If there's no police report and nothing was ever filed with insurance company then it's a case of he said she said. Is there any damage to your vehicle wether it be dented bumper paint from her car scraped off or anything. If there's any unrepaired damage to your vehicle then I suggest you get it fixed quick and make sure there's no sign at all of you ever backing into her and then there's no proof that it was you could have been anyone.