I would automatically assume there would be more legal implications if she were out in public and deployed the dog or the dog bit because the guy crossed some boundaries. Especially if the dog bit and there were no witnesses…etc. He/said, she/said is never a good scenario especially for the dog.
On the other hand, if the guy is on your property and you have a sign posted I would assume that you would be a little more protected by the law. I train dogs and have trained protection dogs that are not just “dogs” they are our companions and part of the family. With that said if I have to I will deploy my dogs in a heartbeat; if they had not already picked up on the possible threat and alarmed.
My dogs are much more protective when alone with my girlfriend, they will bite but they are also trained to sound or ‘bark’ on command. Even if your dog is not protection trained I would invest some time and effort into training him/her to bark on command even if he/she won’t bite. I don’t know many people that have enough courage to walkup on a barking dog even a small/medium size dog. Often protection training is not needed…barking dogs can be extremely intimidating. Just ask a mailman
I am sorry I can’t answer the question as related to the legal aspects of the dog biting.