Yeah, I mentioned Glock mostly for weight reasons. A M&Pc is smaller than the 19, but weight is similar.
So going with a smaller pistol than a 19 is no guarantee that the pistol is lighter.
I have heard more than once that between a M&P shield and a 43, the slightly heavier and touch larger shield is more comfortable to shoot. The shield is about 4oz lighter than a 19.
The 42 is chambered in a weaker 380 round, but the small size makes it shoot similar to a 43 in 9mm.
If weight really is a concern, the 26 may be the lightest and smallest that is still comfortable for most people to shoot.
If recoil is less of a concern, then a shield or 43 may be good options to get small and light carry. (There are other pistols in this size and weight range as well, the Walther PPS gets praise as well)
Is you 19 a gen 3 or 4? As a gen 4 is smaller in the hand, and may feel better for her than a gen 3.
As far as a safety... I find that teaching how a firearm works mechanically, goes a long way toward easing apprehension.
If you are familiar with how a glock functions mechanically, and how the parts fit and work together, it's easy to show how it's basically physically impossible for the gun to fire unless the trigger is pulled. After that, safety lies with the user, as it always does. A user can forget to engage the safety or bump the safety off, just as they can misplace a trigger finger.