You don't understand the purpose of a protective order. It isn't going to keep a severely agitated person away in many cases, but it may keep someone from coming around and then losing control.
I'm not saying the OP's sister should not get a protection order. As long as she understands the order will not necessarily protect her from anything. The problem with protection orders, in most jurisdictions I'm aware of, is that the consequences for violating such an order are little more than a slap on the wrist. The defendant is usually released from custody the next day. There definitely should be stiffer consequences for violating those orders. I agree that the OP's sister needs a comprehensive security plan that involves the court, law enforcement, family and most importantly, her own instincts
. Becoming proficient with a firearm, would be just one very important part of her overall security plan.