A lock on my front door doesn’t stop someone trying to break in and rob my house, either, but it does discourage it.
If someone starts leaving garbage on top of/next to the dumpster we’ll come up with a new strategy. The local municipality would be happy to issue monetary penalties to guilty parties. Among other possibilities.
So? It’s Wednesday. What’s the scoop? 
While this might be satisfying to contemplate, you might be running afoul of the law, here, by signing them up without their consent. You might also be breaking a law if you raise their rent without a new lease.
I think that you’re morally justified in doing either of those actions, but they might not be legal.
Well, a (non) update for all of those who are on the edge of their seats about this (heh!): either she didn’t do it this morning because there was no school and therefore no time she knew I would be gone, or word has gotten out that I’m pissed about this, and so she has stopped.
I will keep you all posted as further developments occur. . .
You know, just so you don’t lose sleep. 