there are alot of options in that price range. What kind of blade style do you think she'd like? A SD knife and a small knife dont exactly cross paths together in my mind. In a SD situation if its burried in her perse and not in her pocket it probably wont do her much good.
My fiance likes the Kershaw Mini-Mojo I gave her and she uses it at work. If she likes colors other than black the Kershaw line of Leeks, Chives etc have all kinds of colors and are assisted opening. The assisted opening is nice as its easy deployment and the leeks and chives have little plastic slips that can help keep the knife from opening in her purse.
There are other options, for a little more than 50 you can get her a spyderco delica or under that theres the Spyderco persystence. Boker has some nice options for under 50 like the trance or there more SD oriented BAT but I think that may be a bit larger than your looking for.
The biggest thing for me was to give my girl a knife she not only liked to hold but felt comfortable using, for whatever reason she loved the lock on the mini-mojo and preferred it to the liner lock.