Catherine didn't expect Helen Blair, who usually seemed weak and fragile, to have such a strong attitude now. She assumed Helen would be as easy to deal with as Jane Howard. However, when Helen spoke her mind, Catherine found herself at a loss for words, unable to retaliate because what Helen spoke was indeed logical. Her father wouldn't support her in creating a scene. Last time when a similar issue happened, her father was deeply displeased. If she were to stir up trouble this time, her father might get angrier and could even cut off her allowance, which would be a severe punishment.
Moreover, ever since Helen defeated Elena last time, she has been highly valued by the school. The school certainly wouldn't want a student who has a promising future in the National League and could bring fame to the school leaving.