one of the tip-up barrel Barrettas? I know they are only in 32 and 380, but any gun is better than none, and it would eliminate her having to even rack the slide. I am currently looking for one for my wife.
A few months ago my wife and I went through the same process you're researching. We took a trip to the local range with two firearms instructors who brought more than 30 different handguns along. She needed personalized instruction and I was there for moral support. She shot everything they had and it really helped narrow it down. She shot more than 100 rounds through the S&W .38 Target Masterpiece from a bench rest. This helped her alot.
She shot the LCR and LCP for reference and then the SP101. She was very comfortable with the SP101 with .38 Specials. It fits her hand. It's point and shoot and we save money on ammo because I like to shoot it also. She's confident to use it if needed and I think that's 90% of the battle.