Board Thread:General Discussion/@comment-1616746-20140525022058/@comment-24901406-20140525195117

The sister who appears in the movie is not Wanda but another sister (possibly Lorna but that hasn't been confirmed and would take some liberties with the source materials and timeline of the movies), although Wanda apparently does exist in this universe as well but wasn't shown.

Inevitably this is the curse of the sequel set up, Evan Peters is signed up for X-Men: Apocalypse so they leave all the development for "the next movie", then never bother doing it there either.