Well, Ina is well known to her with a few current and pl collabs. And Calli is probably one of the most approachable major vtubers out there whom Henya has mutual friends with. So, not really that surprising.
I think that having someone Henya already knows to break the ice works quite well. See also her collab with Pippa, where her old friend Tenma was running around being a gremlin in order to take some of the the pressure off.
