Moff Gideon shot Bo-Katan. Koska Reeves was initially standing closer to where Gideon was sitting, but moved closer to the blast doors as the Dark Troopers were battering it. Bo-Katan was looking at the monitor watching Luke in action when Gideon pulled the blaster and shot her. It seems like the Beskar in her armor took the brunt of it, and Gideon also shot Din Djarin in the process of trying to kill Grogu.
When I first watched the episode it seemed like there was the possibility that Moff Gideon might have killed Bo-Katan. I know that I was distracted by Luke continuing to cut through the Dark Troopers. But when I watched again I saw Bo-Katan get up.
Gideon's exchange with Bo-Katan about the Darksaber seems to have made Din Djarin's world significantly more complicated. Bo-Katan made it clear that she wanted to face Moff Gideon. And Din Djarin was fully prepared to give the Darksaber to Bo-Katan. But Gideon's knowledge of the Mandalorian customs associated with the Darksaber indicates that if anything, Din Djarin is potentially in line to be the ruler of Mandalore having won the Darksaber in combat. If Gideon had killed Bo-Katan things would be a bit more clear-cut. But it seems clear that Bo-Katan wants to rule Mandalore. So will she continue to be an ally, or become an adversary of Din Djarin?