What did the incident with Niang and he baby tell us about her? Why was Adeline the only one who tried to stop Niang?

Essentially, the baby is afraid of Niang because she doesn't know her, but Niang, as usual needs to be controlling and do things just because she wants to....... the baby doesn't want to be picked up, so she picks her up; the baby throws a tantrum, so she slaps her. Adelaide, on the other hand, is the only one present who speaks up and does the right thing by telling her to stop. Everyone else stays quiet because they do not have the same kind of forwardness and because they've been raised not to question the actions of a parent.