Due to the death of Carrie Fisher Disney's original plans to wrap up the sequel trilogy seemed to have suffered some issues, as episode 9 was originally planned to be fairly Leia-centric (in the same way 7 had a lot of Han and 8 probably will have a lot of Luke), and they largely had to scrap the original outline of the story (It's unclear if the new direction was why Tremorrow left).
There's been some recent pictures of Laura Dern's character addressing what appears to be a Resistance briefing, and she's referred to as an admiral so I'm wondering if the character will somehow take over Leia's leadership role in the resistance now that Carrie is gone. Interestingly, in ROTJ, Leia's leadership ability was largely diminished from the first two episodes; in ESB she's practically co-leading the base with Rieekan, for instance. In ROTJ she seems to mainly just be another rebel soldier, with Mothma, Ackbar and Madine doing all the heavy lifting so to speak-she doesn't even know that Han is leading the strike team. ("I wonder who they found to pull that off?"). So maybe Holdo's a bit like Mothma in that regard?