Is it right for me to feel disappointed about the way this girl is acting?

So I guess I should start from the beginning. I currently have two jobs at the moment; they're both at dental offices specializing in different things. One of my offices was looking for another assistant to help during the week day since I am only doing part time. Well, the doctor had asked me to look around to see if I could find someone who'd be willing to do it. I had a friend who had dropped out of dental school 2 weeks right before she was to finish the program & earn her certificates. I had addressed this w/ the doctor and she said it was fine but she wanted to talk to her. I told my friend to come in for an interview and it apparently went great. She started working that same day for 7 hours. At first, she was excited. She promised to not let me down, embarrass me or made me look bad; It's barely two days later & I got a text from her about 2 hours ago saying that she wanted to quit! Here's the thing: she doesn't want to tell the doctor straight up and she was just going to stop coming in. The reason? The doctor wasn't going to pay her until she got her certificates. I told her straight up that because she's not in an internship program or in the process of getting her papers, that in order for her to get paid, she needed her certificates and she just bluntly told me "by law, I AM supposed to get paid." Is it right for me to feel disappointed in her and to feel like she just totally betrayed me? Or am I just over-thinking it? I've stopped talking to her for the last couples hours to calm myself down but I still can't help but feel this way.