Based on her appearance in The Mandalorian, it is clear that Bo-Katan his still keeping tabs on her old friend Ahsoka from the Clone Wars. And if that is the case, then it would make sense for her to make an appearance in her spinoff as well.
In The Mandalorian, Bo-Katan instructed the titular character to head to the planet Tython to find Ahsoka to help him locate a Jedi.
Seeing as she knew what planet Ahsoka was on as a part of her adventures around the galaxy, then the two may still be in some form of contact. And as such, if Ahsoka was ever in trouble, Bo-Katan could be someone she turns to for help, or vice versa.
Bo-Katan’s next move following the finale of the second season of The Mandalorian is still unknown. However, with the third season likely being delayed until 2022, then including her here would be a great way to help tease what to expect in the upcoming season.
All these shows are going to be interconnected (The Mandalorian, The Book of Boba Fett, Ahsoka and Rangers of the New Republic). And because of that, Bo-Katan makes as much sense to cross over into Ahsoka’s series as any other character.