Wow-thank you for all the replies! I really appreciate all the feedback
I don't know why she offered to go outside insurance. This happened back in November. She was obviously an intelligent woman and of some means. (Big ring-turns out she is married to a Dr.) Maybe too many claims? I don't know. She did say she thought it was just the bumper and it would only cost a couple of hundred bucks. I knew better, and said that my deductible was $1000 and if it was any more than that we would have to go through insurance.
I didn't hear from her for over a month and thought she forgot about it. She said she had been busy and would get a couple of quotes. I didn't hear from her again until Tuesday. Her husband called, was nice enough, but said bill was $900.
I get the bill and I wonder if it's trumped up. Four and a half hours for painting-am I paying for the guy to watch the stuff dry

Look, I don't mind paying for what I did, but like mgburg said- I don't feel like I should get dragged through the barnyard.
Pete G has a great point that I didn't even think about-what if they do come back with some BS injury claim? But I agree with TW-I don't think they will and it should be fine.
After reading this, I'm leaning towards just paying them. It's my fault, and I've already inconvenienced them enough. It sounds like bumper work is dreadfully expensive. And I don't have much to gain-if I go through my insurance I still have to pay the full amount and I ruin my perfect driving record (and raise my rates). Besides, isn't it too late for me to file a claim? I should be less ignorant.
The bumper is most likely damaged-you could see the bolts pushing through the plastic cover. (Sorry, no amount of buffing was going to fix this) Even though I was just rolling, the 300 is heavy, solid- a nice hammer