Boobra

Answer: Ron having a horrible time and berating her for being "with the enemy" had her upset. Plus the fact that there is a growing attraction between the two that has been evident since the second movie, she feels that he should have seen her in a different light and not just a "convinience" date to ask at the last minute.

Boobra

Answer: Hermione does tell Ron that the next time there is a ball to work up the courage and ask her before someone else and not a last resort.