If you really need an answer that badly,then why don't ask her about this? If she doesn't tell you the reason and starts chatting next day tell her 'I was waiting for your reply all night and you stopped chatting suddenly now you are dead for me,bye'(sounds a bit harsh but it seems that she doesn't give a damn 'bout ya and your feelings ;-( )

1. It could be the chatbox on italki not working properly or any other technical problem. MSN and skype can do it to you as well. Messages just get lost. 2. Could be a cultural thing. I've noticed that Americans often go offline without saying "good bye". At first it was shocking to me because we never do it in Russia. Then I got used to it. Maybe it's normal in her country. 3. A personal thing. Some people take chatting here more seriously than others. A lot of members here are quite light hearted about the whole thing.