Vanessa, you are close.
(I studied copyright laws as part of my "senior project" (something you need to do in order to graduate from secondary (that's a global term right?) school.))
(That was a lot of parenthesis haha)
Seriously though.
The Berne Convention is a treaty across 165 countries that states that anything you create is yours. You automatically have the copyright.
Which means if, say, she didn't take the pictures down. You would be able to send her another message threatening to take her to court and sue her how ever much you want to. $1,000 is a nice scary number. That would most likely scare the crap out of her and cause her to take the pics down.
This is the sucky part though. If she instead said, "That's fine, bring it on," You couldn't do squat.
Not only would you need to shell out a ton on a lawyer, but after paying for your first consultation your lawyer would tell you that you have already lost the case. Because even though you own the copyright, you are the only one who knows that for certain. There is no way to prove that you took those pictures and not her. If there was, then you might win. But a judge could still rule in favor of the girl.
The only way to absolutely, beyond a reasonable doubt, with out question, prove that you own the copyright, is to pay to get a U.S. copyright, which then gives you the right to use the copyright notice.
So you can threaten to sue someone because your work is copyrighted (that sound so weird) and not be lying at all. You do hold the copyright! But you would lose if you went to court.
Fun fun, isn't it?