I get the impression Sasha/Mercedes has some dirt that allowed her to get out of her WWE deal with no strings attached, since even Brock had to sue to get out of his back in the day.
She wasn't there because she got injured in the NJPW Strong women's title match. WIllow shoot-won the title since it wasn't the plan for her to be the first champ. Sasha would have made an AEW apparence by now most likely if not for that.