My usual answer to that question is "Use what you are best with." If she's a new shooter, then she won't know yet what she has the most confidence in using. The point of the current exercise is to get her started in figuring out the answer to that question.
I'm glad to see Kathy's site mentioned early in the thread, and doubly so to see Kathy herself weighing in. As long as your friend is physically healthy she shouldn't have any problems running whatever firearm she chooses. I tend to agree that a semiauto handgun is probably the best starting point for her, and that a small or medium frame 9mm is probably a good way to get started for her in figuring out her eventual solution. But as has been mentioned, hardware (toolset) is the easiest part of the process to master. Mindset and skillset are far more important, and take a lot more work.
Please offer her all the encouragement you can!
Mindset - Skillset - Toolset. In that order!
Attitude and skill will get you through times of no gear, better than gear will get you through times of no attitude and no skill.