Lots of good suggestions already. I have three Ruger MK II's, and one MK II era Ruger 22/45 which has a different grip angle than the traditional MK II/III and is polymer. So you see what I like.
What is the purpose of the pistol? Casual target shooting and plinking? Do you think she'll want to get more serious and shoot some competition? If so, the Rugers MK series are nice as they can grow with you with a few, easy modifications from companies like Volquartsen. If she wants something that will feel more like a centerfire pistol to go in that direction, a Ruger SR22 or even a 1911 style .22LR may be the way to go.