Take her to a range that rents guns
This without any question.
Fwiw - I taught a 70+ year old woman with multiple sclerosis last fall. She tried several 9ís and settled on the M&P Compact 9 2.0.
fwiw - a mid-size pistol is easier to control than a subcompact. Folks show up with Glock 43ís or Shields and leave to buy G19 or M&Pís.