You said she didn't complain, and she stayed with you for over seven hours before falling asleep on the couch. It does not sound like she "acted like she was tortured".

Here's my problem with this whole thing--- while you love LOTR, you have seen the movies many times and you even watched the first two with her recently. So you need to be honest with yourself about your actual motives in asking her to sit through them again for your birthday. You didn't ask to have this LOTR marathon for your birthday BECAUSE of your enjoyment of it, you picked it specifically because you're upset that she DIDN'T enjoy it and you want her to change, and you thought your birthday would guilt/pressure her into doing so. That's what makes it petty. (Your unspoken expectation was tantamount to "You'll sit there and cook/eat broccoli until you LIKE it, dammit!!")

Stop saying she didn't try. She's not trying to change her mind (after all, she did watch the first two movies with you a few months ago) but she did try very, very hard to be supportive of you. She made you a birthday cake and sat with you on the couch, while bored out of her mind, for over seven hours before falling asleep, and she didn't even complain(!). Do you think this was how she wanted to spend her weekend? Sitting next to a grumpy AH who's reading into her every move and getting resentful and pissed at her when she did nothing wrong?

Her only mistake was believing that you wanted to watch LOTR because you like it, rather than wanting HER to REWATCH it because you're upset that she hates it.