I have the SR9c and am very happy with it. I have fired several of the SR series, and liked them all. My daughter also has one and it is her every day carry gun. She has small hands, and has no problems firing it. It should be a good choice for your sister.
A bad day at the range is better then a good day on the job!
I love my SR9C it's reliable and extremely fun to shoot. I conceal carry it a lot and I'm happy I bought it. As soon as I saw it I knew it was coming home with me. If your considering buying one do not hesitate. You won't regret it.