Originally posted by: kAi
Chapter 139:
"Kakashi-sempai, you are here for obito-san right? Your always late for examinations. is it because of some special cause?"

she would know why he is here if it were rin.
And to add on to that, sempai in japanese means like an older schoolmate, it translate into something like Learning brother/sister kinda thing. If they were on the same team she wouldn't call Kakashi "Kakashi-sempai", it would just Kakashi without the sempai.