trope of MC being 'thrown away' by a idiotic prince, obviously being used by the large marquis here. And regardless if he was thinking she was mocking him behind his back well... yeah hes stupid enough.
So world has Dragons and/or people related to them who looking for mates, clearly the Emperor who spoke for MC knew she was innocent and probably inflicted a powerful ''curse'' on the marquis and crown prince to leave her family alone.
Possible guess that the marquis was going to try buying her later, but no one expected a random to pop in within the same day.
Guessing the Knight Commander is clearly part dragon and MC is is 'fated' mate.
atm though going to be hard to tell if her family will accept her back, usually the trope is the family has noses up and says screw you.