Dave - LH playing opens a can of worms that no one will agree on.
Borrow an ordinary guitar and see how she gets on - go to a teacher and discuss alternatives.

If her level of operating disability is not too high she will play 'normally' without too much trouble.

You can reverse your handedness on the guitar (as most LH players do) but do spend a few weeks or even days trying with minimum modification.

Stu