My current hypothesis falls between the extremes of “Wanda is totally in control and is therefore the ultimate villain” and “there is a Big Bad who is controlling everything and Wanda is therefore a victim like everyone else.”
I believe that Wanda is in control of the simulation/fantasy, it’s her magic that is manufacturing the bubble, but that she has been misled and manipulated into doing so. It’s her power, but it’s being deployed under the influence of the (as yet unrevealed) ultimate villain.
This creates a much more nuanced, shades-of-gray situation, compared to the either-or absolutes of “she is using her powers purely selfishly and destructively and cannot be redeemed” versus “she has no agency in this at all.” When she’s genuinely confronted with the reality of what’s happening, the torment being visited on this town, she will be horrified and penitent, and will need to turn on whatever is manipulating her. But she will also need to atone, in some way, because she does bear some responsibility.
We know from sneak peeks that Wanda will be involved in the upcoming Dr Strange movie. I strongly suspect that Strange will appear near the end of this series, either to offer assistance with this obviously mystical trans-dimensional threat (“Why didn’t you contact me sooner?”) or to help clean up the mess afterward. He will offer Wanda sanctuary and tutelage, and that’s where she’ll be in his movie. (Which offers a nifty correlation between the trajectory of his story and comics precedent. At the end of the first Strange movie, Mordo says, “Too many sorcerors,” pointing to his future path. At the end of the House of M comic, Wanda says, essentially, “Too many mutants,” and forcefully cancels the powers of huge numbers of them. One wonders if her arc in the Strange movie will reflect this, as she decides whether or not she agrees with Mordo.)
Oh, and on that point, I would bet a substantial amount of money that the villain reveal will not be Ultron. We’ve already done that, and it would be a repeat. Yes, recurring villains are a thing in the comics, but Marvel’s strategy for on-screen stories has been to expand its canvas and its roster. It’s true that a reveal of Nightmare or Blackheart or Mephisto or somebody would require some introduction, but we already have a built-in model for that, with the appearance of Strange. All he has to do is reference Dormammu, and say something like “there are many such beings in the multiverse, and some of them are worse,” and we’re primed to understand what we’re getting into.