Is hacking into someone's Facebook a federal offense?

My friend's Facebook was hacked today and I know the person who did it. Apparently the girl who did it was a stalker and is nuts. She hacked her account and told me to kill myself then I found her out and she flipped. She called my friend and said I am suicidal and was going to do it. I know Facebook now has everything threw chat go to your inbox so that is email and tampering with mail is a federal offense the law isn't exact what mail they are talking about, email or mail. Can someone tell me what this girl can be charged with if she can?