Thanks for all your replies.
As some mentioned, the caliber will work -which was my main concern - but the difficulty of getting the rifle "on target" quickly is also an issue. Plus, I know that she won't want to carry a 7 lb rifle around all day; slinging it will just make it harder to use if needed.
I guess we're back to having her carry a revolver. Now, I have to find a caliber / weight that has enough energy to do the job at very short range without the recoil making it impractical for her. Maybe a .38/357 with SWC in a SP101 or similar.
I realize this isn't really a "hunting" question anymore, so thanks very much for your patience.