I've been in the same situation with my daughter, when she was in college, a huge (50,000 students) state university with vast parking lots and parking garages. After extensive research, it became clear that nothing comes close to Fox Labs spray, particularly the cone type. There are some Youtube videos of some tough guys being immobilized by this stuff. It's been described as "like somebody dumping a spoonful of fire ants in each eye."
There are several threads on this site containing excellent advice for how to carry and use it. There are definite do's and don'ts.
I don't have any experience with tasers, but have often been advised that they are dangerous because they require the user to get too close to an assailant (within arm's length), not a good idea for a small girl.