Take her to a gun shop that has a P30 in stock. Put it in her hand.

That should be the end of it right there. I did this with a friend of mine who was trying to talk me into an M&P. He shut up the moment he held the P30, and now wants one, too. They're love at first grip with the right backstrap and plates in place for her hand. Have her hold it, rack the slide, try the slide lock, and mag release.. the ergonomics are fantastic, and the recoil system on it is great. It's a very soft shooter. The 40 feels like a typical 9, and the 9.. well.. it's like an airgun, IMHO. H&K has no other gun that can really be compared to it in terms of both feel and function. I was looking at a P200 when I met the P30. I forgot the P2000 existed 5 seconds after I picked up the P30.

The one gun that is a good comparison in my opinion, is the Walther PPQ. I own both of these now. The P30 with a full Bill Springfield trigger job, Trijicon yellow/green night sights, and a Lasermax Uni-Green laser, and the PPQ with a Sprinco recoil management system and the same green/yellow Trij sights. I love them both.

PS My P30 is the variant 3 trigger (DA/SA)