Generally speaking, insurance follows the vehicle (owner) first and driver second. This means with most insurance companies the damage would be covered by her policy primarily since she gave you permission to drive. There can be exceptions though so you will want to check with her insurance to make sure.

If the damage is only to your friend's car and nothing else you will need to make sure she has collision coverage to fix her car. She will have a deductible which might be more than what the 300 dollars worth of damages in which case you might want to pay for the damages yourself.