I agree with HG...most kids will cheat at some point and your daughter was unlucky enough to get caught! I would see why she cheated--maybe she's not getting the material? Or maybe it was peer pressure? Whatver the reason, stress that cheating is never an option and it does her no good in the long run. And stand by what the school decides as punishment. I've seen too many parents fight to get their child out of a cheating "charge" (not that you would) and some were successful--no lesson learned there!
It's a pretty good thing that she was caught now, really. She's less likely to cheat when she gets older if she's already experienced the consequences. In the high school where I taught, cheating was an automatic failure for the grading period and was included in your school transcripts. On your second offense, you were expelled for the remainder of the year! I actually had one senior who committed her second offense in my sociology class (on the final exam, no less), and she didn't get her diploma because she had to take the class (taught by me again!) in summer school. Yuck!