I'd have no problem recommending a 3" .357 SP-101 as a defensive handgun for a woman or anyone else who needs a good handgun.
I own two, both with 3" barrels (although one is for sale now - but the other one is staying!). I've found them to be very comfortable to shoot with Hogue grips with both .38 Special and mild .357 loads. I carry Speer 135 grain short barrel loads for general concealed carry. I also shoot a fair amount of full power factory and handload .357's and although the blast and recoil are unavoidable, the gun is still manageable.
I've taken several friends, including many women, shooting for the first time at college and no one has found the SP-101 to be uncomfortable. And I personally liked them so much that when I got the chance to buy a second one just like my first, I took it! Yes, it was impulsive and I'm trying to sell it now, but I still really love them.
I don't think the 2.25 inch version would be terrible either, but there will definitely be more recoil and blast because of the shorter barrel. Also, the .357 is not at its best from such a short barrel. A lot of the power is wasted because there isn't enough barrel to burn enough powder. The SP-101 is not a lightweight as far as snubbies go anyhow, so to my way of thinking, there is no real advantage in going with the shorter barrel.
Having said that, you're going to have to let her choose what she likes. It may well be something totally different than what you want her to use.
I ran into this with one of my best friends when she bought her first gun. I advised her on several good options, let her shoot all the guns I could lay hands on, and in the end she chose a Walther P22. She wanted it because it is cheaper to practice with and it fit her hand well. I really wish she'd chosen something more substantial, but she didn't. So I did some reliability testing with it, set her up with a few boxes of CCI mini-mags, and practice with her as regularly as possible - which is the best I can do.