That's may be what happens. To understand the situation better, think of someone you work with and know well at work. Some contact outside of work but not much. Then they knock on your door and say, my mother-in-law is at my house.
OK - so she isn't a good friend you would have happily taken in. Unless you want to make a big fuss that will make things uncomfortable at work, you are probably stuck eith her tonight.
It's bizarre behavior, and you know know a little more about her than you did before. ;~D
So what's she doing and who does she think you are talking to on the computer?
How can you be posting this when your friend is there?
Well, if that's the way it is and it doesn't bother you that much, make the best of it and have a good time.
Since you are on FR, that means she is alone in some other part of your house.
Say goodbye to us. Try to have fun with her and tell us how it turned out tomorrow.
If it happens again, though, go the Holiday Inn route.