Same thing happened to me with my suburban. Be careful how you describe what happened. Technically, you changing gear, would be considered "still in the act of backing" and therefor would be 50/50. Colorado bars recovery in 50/50 cases. So you'd be responsible for your damage and she for her damage.
When it happened to me we were both backing up and the other car sustained damage. She gets out and we both agree that we were backing up and met in the middle. Her husband(Larimer Sheriff deputy) tells her to call the police and when the police arrive her story changes and says that she was stopped and in the process of shifting to drive. Cops tell her that the attorneys will argue that she was still in the "act of backing" and that they have been chewed out by attorneys in the court because they thought different.
When I gave a recorded statement to my insurance(She went after my insurance) my case rep, said basically the same thing.. Both of us were backing and therefor 50/50... Which means she can't recover anything from my insurance..