I was thinking the same. I’m not sure what Gotham’s plans are for Jamie, but if she’s going back to that show, then she can’t really pull double duty–even for an episode–on ABC as Mulan which would explain the answer that they can’t get to the Dragon’s daughter this year.
It must be so frustrating for Adam and Eddy when the actors get attached to other shows. Once is actually pretty ambitious with all of its characters but that unfortunately works against it quite a lot as the actors aren’t always featured much and therefore opt for more secure gigs.