Well, if she's really worried about an ex, the dog and/or security system may not be the answer. Is the ex a real bodily threat? If so, dad and his pals, S & W, is probably the only answer. Court orders and the like don't really protect. They simply add a minor charge to a criminal offense.
If the ex is not a bodily threat, a good monitored security system gives peace of mind. We've had one for 20 years and are very pleased. We started with a local company that later sold out to a national chain. We didn't like being monitored thousands of miles away, so we went with another local firm. They monitor 5 miles or so from the home.
I like the alarm system for four key reasons:
1. If an intruder breaks in, we get a heads up and we know the alarm company with dispatch the sheriff.
2. If we hear a noise at night, we can just roll over and go back to sleep. We know it's not someone who doesn't belong rummaging around the house.
3. We like the fire alarm that will alert us to danger and have the fire dept. dispatched.
4. When the family comes home, we know if the alarm is still active, no one is in the house.
Best $20 we spend each month. (Well, next to a UOA

)
Good luck,
Jack