Easy.
Get 4 no trespass signs and put them on all four corners of your property. Sign and date the day after she did the damage.
Now go to the police and file a police report regarding the events, time, date, etc and tell them you have put up these signs because of this event to protect your property.
The next time she comes onto your property she will be trespassing which is a misdemeanor and depending on what state you live in there are fines and penalties (jail time) for each and consecutive acts of trespassing.
OR
Get a new girlfriend.