You know, originally I didn't think that this could possibly be suicide, but what if Zetsu has been turning into Obito and appearing before Rin ever since he's been gone. Rin thinks she's hallucinating because Zetsu runs off and then heads underground and she can never catch up to him. She keeps seeing him all over the place, while Kakashi never does and it drives her insane. The only thing is why use Kakashi's Chidori? She could have commit suicide with a kunai, but perhaps she saw it as symbolic. In the end Rin realizes she did love Obito and now that he's gone she's racked with guilt.