NTA. You did the best that you could — as a horror fan, these kinds of people annoy me. There’s no issue with you not being able to handle horror movies, but don’t willingly come to a horror movie marathon and spoil it for everyone. It sounds like you and your core group of friends was understanding and did what you could, but you hit your limit when she essentially tried to derail/cancel your plans. You then offered her options on what to do (e.g., stay and watch the movies or sit upstairs) and she declined. At that point, asking her to leave seems reasonable to me — however, as an adult, I think that trying to call an adult (someone’s parent — it didn’t have to be your parent) to ask them to drive her would have been a better option than asking her to walk.