Marvel is still in the business of collecting Hollywood stars.
Time to speculate! Who do you think she'll be playing?
(If they come to an agreement, of course).
Princess of the Dark Dimension?
The fan-favorite right now is Clea. She and Doctor Strange have had an occasionally fraught relationship, but she's also a his disciple. Later in the comics, her power is actually greater than his, and she rescues him the way he rescued her at the beginning of their relationship.
Marvel has already demonstrated that they're willing to go for genderbent casting with this film
We have a long time to wait for more solid news about this release, but that just means we have plenty of time to hypothesize!