Chouelle is actually being kind by telling her. i think she doesn’t hate Ersala, she’s just jealous of her but at the same time, doesn’t want her or the emperor to go through the pain of inevitable rejection like she faced, even if her dad broke off the engagement first.
in the long run, this will just help Chouelle learn how to break the curse for real, not just halfway. he should have told her this info privately from the beginning tbh.