I'd like to revise my advice, re: what I would do.
I'd email the TA, and copy the professor AND THAT CHEATING BITCH

. That'll learn her.
😎
I'd love the opportunity to hear a sociologist's perspective on how our society developed the backwards notion that it's okay to steal someone's work (so long as it's fewer than 20 pages, or something
🙄), but not okay to send a clear, unmistakeable message that violating that boundary is completely unacceptable.
Personal war story: a pilot project I did on childhood obesity got a lot of attention last year, and I decided to go through the IRB process to get approval to gather data for a formal study. Another professor blatantly ripped off my protocol and tacked it onto a grant application he had in the pipeline. When I found out, the professor who was guiding me through the process made sure that what this guy was doing came to light. I don't know all of the ins-and-outs of what happened to him, but I do know that he is no longer allowed to be the PI on anything going through my university's IRB, and he has been disbarred from the NIH (he can't get funding from NIH in the future).
The point is, even if people on SDN don't feel like stealing work/ideas/intellectual property is wrong, the professional community takes a pretty dim view of that kind of behavior. This idea that it's unprofessional to protect your work and insist that others not present your ideas as their own couldn't be more misguided.
And I say that as someone firmly rooted in the "real world."