It seems Morgan was uniquely suited to finding her way to Thrawn, given her people the Nightsisters originate from Peridea - and she's apparently been receiving visions from surviving Nightsisters who live there.

Source: https://screenrant.com/ahsoka-grand-admiral-thrawn-sabine-wren-star-wars-history-explaned/

It seems Morgan was uniquely suited to finding her way to Thrawn, given her people the Nightsisters originate from Peridea - and she's apparently been receiving visions from surviving Nightsisters who live there.

Source: https://screenrant.com/ahsoka-grand-admiral-thrawn-sabine-wren-star-wars-history-explaned/

Star Wars: The Clone Wars Season 3, Episode 12, ''Nightsisters,'' surrounded this transformation and marked a new point in Ventress' life.

Source: https://www.cbr.com/star-wars-asajj-ventress-bounty-hunter/

The Nightsisters confirmed that the witches of Dathomir originally hailed from Peridea meaning the race was born in an entirely different galaxy.

Source: https://screenrant.com/ahsoka-dathomir-star-wars-history-maul-connection-galaxy-retcon/

The Nightsisters were lead by Mother Talzin during the events of She held all the knowledge of the Nightsisters and was the leader of their group.

Source: https://www.cbr.com/ahsoka-sets-up-nightsister-return/

The Nightsisters were lead by Mother Talzin during the events of She held all the knowledge of the Nightsisters and was the leader of their group.

Source: https://www.cbr.com/ahsoka-sets-up-nightsister-return/

With the help of the Nightsisters, it could very well be that Thrawn intends to create his own kind of order, perhaps one more like the Chiss Ascendancy.

Source: https://screenrant.com/ahsoka-grand-admiral-thrawn-chimaera-unlike-star-wars-destroyers/