Staying with a revolver is a good idea. The best thing to do is to take her out shooting letting her try different caliber revolvers and find out which one will be comfortable for her to shoot. If she is adamant on having a 22 then try to get her to buy a 22 mag revolver. A little more penetration will go a long way in self defense.
USAF Retired, CATM, SC CWP, NH NR CWP, NRA Benefactor
To preserve liberty, it is essential that the whole body of people always possess arms, and be taught alike, especially when young, how to use them... -- Richard Henry Lee, 1787