Firewalls only control flow to and from your computer to provide security/try to prevent someone from hacking your computer.
IP address is a function of your isp. Firewalls don't do anything about what IP address you present. And it doesnt matter if she(or you) was logged in, if the message board records ip address someone computer savy enough could use it to trace it back to the sender. Even visiting a webpage can potentially leave your IP address(if the webpage owner bothers to record such things)
My advice. Try to be nice to people. Even when online.
ok, my daughter posted something offensive on some obscure cheerleading message board, her coaches got wind of it said they called the message board administrator who is going to get back to them with the name and e-mail address of the person who posted. the message board does have a members area with a log in, but my daughter was not logged in when she posted, we also have zone alarm pro, does that block you ip address from message boards. if your not logged in can a message board identify you?