"Oh that isn't what I meant at all. I promise you that it isn't!" she quickly protested when he said that she might be embarrassed to be with him. She flushed brightly and looked a little ashamed of herself, "I just don't want people to get the wrong idea about you."\
She really just didn't want to damage his reputation as a teacher. It was a hard thing to gain it back when it was lost. Snape knew that better then anyone.