Heart Broken

So...I have truely become disappointed in one of my students today. She is my student assistant and has done great work for me. However, I am missing money from my wallet. I thought I caught her a few weeks ago getting ready to go through my wallet...I didn't say anything but decided that I would not allow her to be in my office again. Today, she was taking books out to my car...books going to Africa...and then returned my keys to my desk. And now I missing $20. I am super hurt! I trusted her...I try to trust all these kids. They come from lifes that are unfair, difficult and unloving. I try to remember that I might be the only Jesus some of these kids see but it's so hard because I open my heart and get hurt. Now I have to determine how to discuss/deal with this. She obviously needs to learn a lesson...but my emotions are high...I'm angry, hurt, disappointed. I need prayer! Guidance on how to deal with this appropriatly.