A couple things to consider:

1) The heavier it is the less likely she is to carry it. Heaver weight also limits on the on-body carry options.

2) On the other hand, the lighter it is the more it will tend to recoil (with some caveats), the less comfortable it will be to shoot it and the less she will practice with it.

3) Off body carry has some very sharp downsides:
a) if a mugger grabs the purse, he's just grabbed the gun as well;
b) it takes practice and a well designed purse to be able to access the gun quickly and shoot from inside the purse; and
c) because of a and b above, it demands a high level of situational awareness and some thought and training in retaining the purse.

----

There's a balance in there, but the Colt Mustang/Sig P238/Kimber Micro are worth having her try because they are compact, light weight, easy to cycle due to the light spring, and surprisingly easy and comfortable to shoot.

Revolver wise, you've got 4 basic options.

1) The alloy frame J-frame revolvers.

They are compact, and lightweight, but that lightweight makes them a lot less comfortable to shoot. They run around 14oz for the exposed hammer models and about 15 oz of the shrouded and hammerless models.

2) The steel J frame revolvers.

They are heavier at around 20 oz for a 1 7/8" Model 36 and 2 1/8" Model 60 and around 22 oz for a 3" - but the extra weight makes them much more pleasant to shoot. The Model 60 can also fire .357 Magnum - but it's a handful.

3) The slightly heavier Ruger SP 101

These run about 5 oz heavier than the steel framed S&W J frames but are very comparable in overall size. It makes them slightly heavier to carry, but more comfortable to shoot. And they are also chambered in .357 Magnum.

4) The K frame revolvers.

These will run around 34 oz with a 2.5" barrel. That's 7 oz more than an a 3" SP 101, and 12 oz heavier than a 3" Model 60 - but they are much more comfortable to shoot, and it's the point where the .357 Magnum starts to become a reasonable option.