that's a tough one - but remember this:

You don't have to explain yourself: you're the teacher. She *earned* her grade, you did not *give* it to her. Have her justify to *you* why she deserves something better than what she earned. Have her collect all her assignments that you returned to her, papers, quizzes, essays, exams, whatever, including a list of days she was absent, and tell her if she can convince you, you'll raise her grade.

Yeah. I sound real tough, don't I?? Believe me, I am not, but this is the type of advice my boyfriend would give to me if I were in the same situation, and I believe it's good advice. Trouble is, it's hard to follow that advice when you're the one who has to dole out the toughness ...

Good luck - and if you have a supervisor or department head you can conference with before speaking to the student, that might be helpful -- there's nothing like talking with a colleague to help put stuff like this in perspective. He or she might even have some helpful advice on how to deal with students like this.