At first, all her friends ARE mad, until they figure out that it was YOU, not her, that sent the mean e-mail. Now they're all mad at YOU, even though you tell them it was a joke. Since you logged on using this girl's account without her permission, you invaded her privacy and probably broke the rules of your school. You could be suspended from school and your computer privileges could be taken away. It's not worth the risk.

Think about it:

Is it okay to pretend to be someone else when you're using a computer? How would you feel if you found out that the person you've communicating with over the Internet was not a kid, but an adult pretending to be a kid?

Is it okay to use someone else's account to send mean e-mail? If you wouldn't send it from your own account, should you send it from someone else's?

What is your privacy worth to you? What information about you (or your parents) do you think is private: your diary? Letters to friends? medical information? grades? how much money you have? how much money you owe?