Not having seen the show, but knowing the memes about marvel comics, I'm going to go with:
spoilers:end of spoilers
That's not Jean, that's a clone's daughter from an Alternate Universe/timeline where Jean Grey got cloned and then died and the clone managed to get married and have some kids. And the clone's daughter looks a lot like OG Jean Grey because of a limited animation range. :-p
Let me know how I did when they answer that one.