There are numerous safe ways to do this. One of the forum members - Indie-Arms, is from S. California and may be able to help you. His thread here:
http://www.indietalk.com/showthread.php?t=29788&highlight=safety
As for my advice on that scene:
1) The safest way is to use a prop, non-firing gun (Airsoft brand or other). You could use a compressed air squib on the actress and have your actor recoil his gun when the squib blows. You dub in the gun shot, add some gun smoke in After Effects, Motion, etc.
2) You might not be able to order these in the socialist state of California, but I use several Blank firing guns from Collector's Armoury. These are stage guns and they can't fire a real bullet. The barrels are also plugged, so even debris/sparks is a non-issue. They use smaller 8mm blank rounds, which eject out of the gun when fired. Looks and sounds great:
http://www.collectorsarmoury.com/Shop-Blank-Guns/departments/3/
The blanks are loud and can be mistaken for a real gun, so be careful if you go that route. I've been using CGI gunfire for the last few movies, because it's quiet and doesn't attract attention. See 2:40 mark of this video for examples:
https://www.youtube.com/watch?v=bi2wLA175WQ
If you don't have programs like After Effects, you can export a frame from your movie and paint/clone tool the gun blast with Photoshop. I did that in my flick THREE STRIPE and because of editing, the gunshot looks convincing. See 6:30 mark:
http://www.youtube.com/watch?v=qWLtdhqZ-3w
Her reaction was enough, so no squib needed; just one Photoshopped frame.
Just in case you want the option. Compressed air squib:
https://www.youtube.com/watch?v=SDgKhci3fBk