If you hit her car, then your insurance will pay for repair/replacement from her car with no out of pocket cost to you.
Of course your premiums might increase but thats another topic.
The main point I wanted to get across is, you're better off letting your insurance handle it. If you were at fault, admit fault.
If you fix her car, then later she can come back and bring up all kinds of crap, medical injuries, pain and suffering, rental car, loss of use etc.
Airbags alone will be around 2 grand, unless you buy used, then you still have to consider the SRS inflator has to be reset, and you have liability if you buy used.
We're not even into what happens if you start getting into structural damage behind the bumper cover. I.e. crash bar, absorber, bent core support etc. Just because it "drives fine" doesnt mean that it needs a unibody straightening or you have a bent strut tower. This all has to go on the frame machine to verify.
I'm guessing a 13 year old V6 mustang MAYBE has a fair value of 2500-3000 Dollars. But for your own liability, you may be safer sending this to your insurance company.