If the injured person files a lawsuit against your girl friend, her insurance company will hire a lawyer to defend her in the suit. That lawyer will advise her whether and when to return to Massachusetts for the case. If there is no lawsuit, and the claim is being handled by the insurance company alone, they will advise her as what she has to do and the process that will occur. It sounds like a minor injury case which should be able to be settled by the insurance company without alot of fuss.
If the home is owned by you, and the guest was injured as a result of a dangerous condition on the premises, you are potentially liable for the person's injuries. If you have homeowner's insurance on the property, you should give notice to the insurance company.
In order for the person to recover, they would have to prove that there was a dangerous or defective condition on the premises which caused their injury. Just because someone trips on the property does not give rise to a...
Rather than sue your friend, why don't you just ask your friend to cover the property damage on the vehicle. It is possible that if he or someone in his household owns a vehicle that the insurance on that car may provide property damage coverage for this loss. You should explore that possibility.