How did my mom get into my Facebook?

[Stewie]

Either-

1. She got on your computer and you have your password saved on it for fb.

2. If it was not private, like under someone Status or under a Picture, then if she is a friend of a friend, then she can see it if you do not have your privacy setting strict enough, or if your friend does not have it strick enough and she can print it.

Now if you had this conversation on a CHAT, or on a private Message, and not public like under a status or picture, then she got into your computer via your password.