It was clear that she's on edge 24/7. She really has no one at the palace, surrounded by wolves which want to eat her alive. Her mother's death (more likely assassination) is obviously unresolved too. The blonde siblings were trying to undermine her authority (stepping on her dress is one, making a scene is two). There's also mentioned a betrayal from the black haired guy. No wonder she's angry and bitchy to everyone around her.
Her reaction to the maid is a bit excessive tho, so maybe something happened before this luncheon. Maybe the maids were feeding information to her enemies and she knew it.