If you notice the thread entitled "Is the .22LR enough bullet" I am making the argument that the .22 is not the idea defensive round. The .22 magnum is way better than the .22 long rifle but still isn't the best caliber to incapacitate something quickly.
Anything, including rocks, sticks and air rifles are capable of stopping/killing/incapacitating a threat in short order IF you use them in an effective way. If your lady friend has the ability to handle this weapon effectively, even under stress then yes this is a viable weapon. BUT I would make the suggestion for her to us the most effective caliber that SHE can use properly.
Me personally, I would feel comfortable using a .500 s&w for a defensive handgun but I cannot use this round properly as I, like most, would have problems managing recoil. So I use something less effective because I can use it more effectively.
So I would say that if she is limited to a centerfire weapon then this would probably be a effective weapon. A large capacity and the .22 magnum.
This being said, I have not ever handled, shot, read reviews on the brand or firearm you are talking about so I cannot comment on the quality of it.