I think the Jedi in the trailer is most likely there to throw us off. Inside the universe its only really been 5 years since the downfall of the empire. I don’t think there are any Jedi besides Luke. I’m guessing she is an agent of Moff Gideon. Inquistor???
People also said that “It’s time for the Jedi to end” in TLJ and Palpatine’s laugh in TROS were there to throw us off, and look what happened there. 😉
Although I agree that she probably isn’t a “true” Jedi in the traditional sense, her outfit seems much too dark for that. Maybe she could be a surviving Inquisitor, or some type of Dark Jedi.