Ahsoka was referencing the events of ’ Holocron Heist arc, during which bounty hunter Cad Bane stole a Jedi Holocron containing data on Force-sensitive newborns from all over the galaxy.

Source: https://screenrant.com/star-wars-rebels-episodes-clone-wars-season-7/

Often working with famous characters such as Cad Bane, Aurra Sing was one of the best bounty hunters around during the war, managing to infiltrate the Senate building with a team of other bounty hunters.

Source: https://collider.com/minor-star-wars-characters-ranked/