Originally Posted by AniMeFaN
I think she was a spy and they didnt want them getting the body and any info that would come with it
Maybe, but Zetsu did mention something about the Mist dealing with experimental bodies and somehow, Kakashi and Rin were surrounded. Maybe Rin got captured and Kakashi ventured out to save her, but she was too far gone, so he had to kill her or some shit, IDK.
Obito with Mangekyou powered by the spiral looking Zetsu is obviously powerful. Sharingan and 1st Hokage cells synergy. I don't know why Obito doesn't use a body like that now though, considering he has access to all of Madara's goodies...