By the looks of one of the promos. It looks like Wanda was chilling post Endgame, crying that her brother was dead, her BF was dead, black widow was dead(there was probably a friendship there) and 5 years have gone by(I thought by saying “5 years had gone by” would be clear to mean the blip 5 years time skip but apparently not. I’m talking about the 5 year years that had gone by during the blip. Making whatever friends or life she had completely gone) Her mind broke, powers took over.
I think there a part of her that “awakens” so to speak when someone breaks “character” but for the most part, she’s in the dark about this stuff.
I still want to think that Mephesto is a part of it or someone pulled the first string or is using her to some degree. But ya. Those are my thoughts from the newest trailers and the 5 seconds of new information gathered over a 53 second video.