As the game progresses, you end up having to fight her during a boss fight, and you can even recruit her as a summon during the postgame
X/Twitter user @CentroLeaks revealed an event scheduled in the backend of the digital TCG that references A2 and is therefore seemingly linked to a new card drop
The Archmage: Zig-zagged, Marie has access to all Spell cards of the game: not just from Mystics, but from all the other classes as well, meaning she is the only Investigator that can theoretically cast every spell in the game, but that comes at the cost of not having access to level 4 and 5 non-Spell cards of her own class
If you do, skip your next Battle Phase
I think the card really ties this deck together, being absolutely ridiculous with 1) Sylvan Library, by milling cards you dont need and allowing an easy draw two) and 2) flashback cards, by letting you get value out of milled cards