Rather than getting into debating good and bad "intentions", as far as I can tell, the repackager did nothing wrong. Did she strip your copyright notices from your source files? If not, no GPL violation. (Note I haven't actually checked this, but I do note in the email that you quoted that the person directs you to look at the CSS file where you are credited.)
In any case, it seems ridiculous releasing a theme under the GPL. The GPL is for software. How many lines of code were in your theme? I would have thought that one of the Creative Commons licenses would have been a better fit for your themes.
As for your use of the copyrighted movie image without permission, I'm afraid that saying that fan sites use it, or that you don't intend to make money from it, or that you thanked them profusely for it in your README file etc won't protect you in a court of law. The only thing that will protect you is written permission from the copyright holder. I presume you haven't asked for such permission because you know that they won't give it to you.