Pretty sure it was just her whole terrible attitude - questioning the Duke and Chiffon's judgement (including to the Duke's face in Ch.17); pretty actively disrespecting the people they're trying to build relationships with, etc. etc.
Acted way outside of her station. The result is a very rare sight for an isekai i'm not gonna lie. Usually rabid harpies like her are played for laughs but she got dismissed almost instantly despite being with the princess since she was little. Now she is being a bitter loser about it. As long as she lacks the necessary retrospection, i don't think she will ever be reinstated considering someone seen her "tantrum" with Miyabi as well. She is just digging deeper.