Any youth model shotgun loaded with buckshot should be fine. If you're into handguns a Glock is the easiest to use and a 17C has very little recoil. Take her to the range and practice, practice, practice. Make a plan about what to do in an emergency. Practice the plan and rehearse clearing the house. The dog is a great idea. So is all the "normal" stuff that you can do to improve security. Improved lighting, locks on windows and doors, alarm system, hedges, gates, fences, etc. Make sure you discuss the whole situation fully before you commit to a new gun. Some people don't have the "stones" to even think about shooting at someone even if they are a criminal.