The gun itself is good, but please please PLEASE do not just go out and buy her a gun and tell her that's what she's going to use. She needs to go down the same path that most of the rest of us did. Research, handle some guns, research, rent and shoot some, research some more, and choose a quality firearm from a reputable company. She needs to carry a gun that she is comfortable carrying, handling, and firing...and she is the only person in the world who can make that decision
I used to own a PX4 9mm subcompact and I liked it. Good capacity, good shooter, reliable, accurate..as expected from Beretta. While it is a "subcompact" it's not a tiny gun by any means. I'd say the same about the gen 2 SIG P250, which is what I carry these days (subcompact .40). It's the nicest shooting subcompact .40 I've ever owned/shot, but some spicy self defense loads will remind you that it means business