It sounds like the problem isn’t that she refuses to watch erotic movies with you anymore, but that it doesn’t happen as often as you’d like. Instead of trying to direct her (“I had her pick out…”), have a conversation in advance. Ask her if she still enjoys watching sexy movies with you, and if so, what kind would she like to see?
It’s possible that her tastes have changed, or maybe she’s uncomfortable about comparing her body with the impossibly perfect, young porn bodies. (If that’s the issue, it’s up to you to tell her how sexy you find her body!) The only way you’ll learn why she’s not as eager as she used to be is to ask her. Make sure you convey that you’re honestly interested in her answer, not that you’re pressuring her to go along with your wishes.