understanding is not agreeing

i have a class with a girl, who is a complete know it all.
she always has the opposite answer then everyone else, and i am starting to think she doesn't really believe that answer, she just wants to be difficult.
we were in the same group and we were given a question about attachment.
she, of course had a different answer then i did, and the other two girls in the group.
it was frustrating because she didn't pick the best option, she chose the option that was easiest. that was not the point of the assignment, but anyway.
the reason for this posting is because she said to me, 'i don't think you understand.'
ha, okay, it is not that i didn't understand. i didn't agree, and then i realized that is what people mean when they say, 'do you understand.'
i didn't agree with her, so obviously i did not understand...clearly. can you read the sarcasm.
i thought of my dad when he says to me,'do you understand me,'
'yes dad, i understand you, but i still don't agree.'
and then he keeps saying the same phrase over and over again until he is sure that i 'understand,' him.
it also made me think of the one and only frank martin, head coach for k-state mens basketball, 'you understand,' is like his catch phrase. he doesn't say it to his players to really know if they understand, he says it to them because he needs to enforce fear, and make sure the player agree with what he is saying, and they can't defy him, because that my friend is disrespectful.
so, understanding is not agreeing, i understand the girl in class, i understand my dads point of view, i just don't agree.
don't get the words mixed up, they are totally different, i mean, 'understand,' alone has five extra letters and one extra syllable.