A revolver cylinder opening to the left would favor a right handed shooter.Beretta Px4 - G model
three sizes, has grip inserts so that you can adjust it to the size of her hand. Standard, compact and sub-compact. What I'm going with right now.
Ambi decocker is standard, mag release is easily reversible.
I haven't looked at them all, but I've never seen an ambi slide release.
The old S&W all metal semi autos (models 39 and 59 and later series) have factory ambi safety/decocker.
Beretta 92 has ambi decocker/safety, and mag release can be reversed.
Of course the ultimate ambi handgun is a revolver. Note that the cylinder on a revolver opens to the left, and favors a left handed shooter for reloading.