Look around your local ranges and bigger shops. We have a shop that for $10 you can shoot 3 diff pistols to see what you like. You want something that will fit but if you stick with the 40 and go with the sub compact it will likely recoil too much for her. I have a glock 23 which is the midsize and I love it(just put nite sights on it). Itweighs about 26oz unloaded. You might try the Kahr lineup. Kahr makes a very good compact 9 and 40.

Irecently purchased the new Ruger LCP, it is in 380,it weighs about half that of the glock (10 oz) and would fit nicely in a purse. As the officer said a good 410 would be good in the house, but she would likely carry a smaller pistol like the LCP more often than a heavier glock. Hope this helps.