My mentally ill friend keeps stealing from me. What should I do?

I have a friend who I'm pretty sure is mentally ill. She displays really weird thought processes about the world and her place in it. She also has a very sad life: she has no education, her mom is a crack addict who neglected her, she got pregnant at age seventeen and does not have custody of her child, she is addicted to booze, her is very promiscuous, and she's about 50 pounds overweight. Part of me takes pity on her, but a bigger part is enraged that she keeps screwing me over. The last time I let her spend the night at my apartment, she snatched 150 dollars from my wallet. Should I call her and confront this behavior even though she always denies her guilt? Or should I silently write her out of my life?