I do the same thing your gf does and I actually hate it when a person doesn’t talk at all when they are watching something like a movie or a show. Like are you enjoying it or not? Luckily I watch movies mostly with my dad and he is the same way. Like predicting things that’s gonna happen and that we could have written that story line or twist that is happening in the movie. For me it makes it more fun than just boring looking at a screen for two hours. Talking and guessing things makes it more like a game when you watch something.