From the choices -
1. 38 snub with the mildest ammo you an get
2. 9mm Kahr if it is the size of CW9 or K9. any smaller may not be fun for first day.
Most important - Have fun.
If it is fun, she might want her own gun.
Do not make it too fun for she will want a 1911 in 9mm with FO front sight and reloading equipment.
I may have been pushing it a little bit on the reloading equipment.