This is one of the reasons I hate writing e-mails or messaging. Words are given new meaning and it is really easy to misunderstand what a person is really saying. I can't even tell you how many fights I have gotten in with friends and my kids over MSN because of a total miscommunication. If I were you I would talk to her and tell her how you read the letter, and how you sensed sarcasm in her tone. I would also give her a chance to explain herself instead of ignoring her. I did not read the letter so I don't know what it was sarcasm about but give her a chance to explain herself. You should would wait until you cool down a bit before talking to her so you don't say anything you regret.