I agree with a lot of this. My first time going to HHN I went with my then-boyfriend-now-husband and didn't want to act afraid, but I really felt uncomfortable quite a bit. We hit it hard since we were with his family and I wish we had been able to ease into it. I've gone for the last seven years and have grown to enjoy it, but I also know my limits. Like TheCode said, it really isn't just jump scares and light-hearted fun in the scare zones. We all have things that really mess with us. For me, that's zombies and certain noises. The massive Walking Dead house that felt like it would never end had me close to an anxiety attack, whereas other houses were a relative breeze for me.
For some people, certain visuals can stick with them. If that movie messed her up that bad, it may be a really hard sell. And the smells can be an issue if someone has migraines. Same with strobes.
I'd run all of this by her if you are going to try to convince her. Maybe show her a couple of videos on YouTube. Last year we went with a friend who doesn't love events like this and had only been to HoS. The YouTube videos helped her feel more comfortable and have things to look forward to (the ball drop in Vamp '85, snacks, etc) and I read up on here for reviews of houses so I knew which ones would push her limits too much.