38 or 357 revolver, load with 38's for practice if 357. The bigger (thus heavier) the gun, lower the recoil. Train her to pull the trigger until she's fired all cylinders or the threat is incapacitated. Most encounters will be 3-5 shots at 3-5 feet in 3-5 seconds. Make her practice from concealed carry. Make her practice on a human silhouette target to condition her.
When I first got into the business a very wise man told me the only revolver was a S&W or Ruger. Maybe other brands have established themselves since, but I have never tried them.