[Well she knows Luke was attached to Obi-Wan, and she knows he's learned something from him, but how much he learned is something Leia doesn't really know. She doesn't even know much about if Obi-Wan and Luke knew each other well before her call for help.]

He did, for a while at least. I don't know much about how close the two of them were, but Luke did seem fond of Obi-Wan.