Question about facebook?

[St.3240]

If your message was small, then she probably only read it in the tab rather than opening it.

For example if you wrote "hello" you can see it in the preview tab because its just one word. If you wrote a long sentence, she would need to to open the mail to actually read the whole thing.

If it doesn't say "seen" she has not clicked to open the mail, but like I said if the message is small enough to be read in the preview tab then she doesn't actually need to open it. So until she opens it then it will say "seen"