I've got a similar problem. Several years ago, my wife swiped my Glock 26 after I let her shoot it. She's pretty good with it, too. The problem is that she won't CARRY it. It sits in her dresser drawer, mag loaded but chamber empty, but our bedroom is the farthest room in the house if she is in the living room and "something happens".
You basically have two options. Either buy her a pistol (or revolver based on HER preference) and have her carry it or get a dog as an early warning system, to give her time to get to her gun. Maybe both if she is like my wife and won't carry even after she has a gun. Her actually carrying the gun would be best, but I'm sure I don't have to tell you about women when they make their mind up about something!
Don't rule out little dogs, either. We have a Miniature Pomeranian. He weighs about 5 lbs soaking wet and would be lucky to be able to open his mouth wide enough to bite your toe. However, he is about the best guard dog I've ever seen. ANYTHING out of the ordinary happens and he is barking his head off. The problem is that he has the "Little Dog Syndrome" and barks at EVERYTHING! You have a warning that SOMETHING is wrong but no idea WHAT is wrong. At least it gives time to get ready for whatever he is barking at, which is about all you can expect out of any dog. The best part is that he is GREAT with our daughters and puts up with a LOT of crap out of them, something that larger dogs sometimes have trouble with.
Bub