Margaery will be going to the funeral, and staying around for a bit of the afterparty. She won't be getting too drunk, but she'll definitely be observing some of these weird rituals and getting a flower crown.

As for the battle, Margaery lives in Sigyn, so injuries are possible? Don't want to hurt her too bad though. She won't be fighting, but she will be on the sidelines, trying out those Lvl 1 healing powers again. She'll also try to keep up morale in her queenly way.