The trailers show Wanda and the mind Stone. Apparently showing her past when she got her powers.
As of Endgame Wanda had no reality powers yet. Just a supercharged version of her existing powers.
I assume that someone else was given powers at the Hydra base, beyond her and quicksilver. That person found Wanda and created this false reality for her. Except Wanda was too strong and hijacked it for herself. That individual is now an unwilling participant like everyone else but can still influence things to an extent.
Edit: That person is influencing Wanda to have kids, so they can regain control of the situation.