In the Marvel comics, Agatha is an ancient sorceress whose story intersects with that of Scarlet Witch in the “House of M” storyline, which was referenced in the very first episode.
This story sees Scarlet Witch alter the fabric of reality after suffering a mental breakdown due to losing the children she has with Vision.
In the comics, it’s Agatha who then wipes Wanda’s memory so that she has no idea she even had children.
Whatever the outcome of the series itself, Agatha’s introduction indicates there are dark times ahead for Wanda.