How to DEAL with a bad employee?

So, I have student workers in my area which I have to manage. One in particular the gives me a headache. I have a great supervisor, and I CAN'T quit. BUT, I can't fire this Young lady either, my supervisor feels sorry for her, and has been FAR more lenient than she would have been with other student workers. This girl gives me a hard time and because I'm young(older than her) AND she's a been a student worker in my area longer than I've been her supervisor, she thinks she is entitled to do what she pleases, including things that only full time employees should be doing..... just because I do something, like take a sick day (I wok 37.5 a week, her 18) she thinks she can call in, slack off or give me an I don't want to or apathetic attitude because I get paid the big BUCKS(not really) even though she is there to be my istant. So, I'm stuck with her, b/c my boss won't get rid of her AND she even let's her advanced to other temp positions(still under me) when they are available. What can I do? This girl doesn't respect me, in any sense. & I don't want to complain too much because I don't want to get into trouble or look bad in front of my supervisor, and TRUST me this girl has TRIED to make me look bad. But I am, how do you say, an over achiever?