Honestly, it gets pretty hard for me to keep track of the Avengers movies. There are so many characters that I'm not even sure when some of them were introduced, or if they ever were. Characters just show up and are all of a sudden in the mix. There's nothing wrong with that (other than the fact that characters get about two minutes of screen time each), but it does get confusing. I remember watching Age of Ultron thinking, "where did Scarlet Witch come from?" Or maybe it was another one of the Avengers movies.
I'm glad she's part of the universe because the odd sexual chemistry between her and Vision is exactly the type of weirdness I crave. He obviously wants to hit that but he doesn't know what to do about it. If that's not a perfect mapping of puberty, then I don't know what is.