NO, don't feel bad, you shouldn't feel bad at all. That just shows your strength as a good person, and her weakness as a not so nice person.
The problem is, we get recognition when we act like jerks, but we don't get it when we act humane, or treat people how one should treat another human being.
This has happened to me several times before, where I'm nice to people and they take advantage of that, mistake it for weakness or whatever, and I end up getting hurt.
But, I think it all pays off in the long run. Like yeah, this girl betrayed me today, but I got a raise a work. I think God, or a higher power, or Karma, or whatever one believes in has a way of making sure everything works out in the end for you. Maybe not when or where or how you want it to, but it still works out.