I think that it couldn't be helped that Kanbaru left Senjougahara. Kanbaru admired and loved her. In fact, She knew that she couldn't help Senjougahara's problem but at least she wanted to do her a favor and tried to comfort her. It was because Senjougahara said outright to Kanbaru that she didn't want to get involve with her again. For Kanbaru, that was really hurt. She didn't leave Senjougahara because she wanted to or had no more intention to help. But it was Senjougahara's wish. And Kanbaru thought that it was the only thing she could do for Senjougahara. If that could make Senjougahara felt a bit happier, she would do it. That was the reason Kanbaru left her alone. IMO
In case of Araragi, he was Mr.NiceGuy who happened to be there. It was because he got involved with oddity before and knew Oshino. That's why he insisted to help Senjougahara and brought her to Oshino. Thanks to his masochist body, he didn't care much about Senjougahara's attitude.
If Kanbaru knew Oshino or knew ways to solve the problem. I'm sure that she would definitely insist to help Senjougahara too. I hope that Senjougahara and Kanbaru can become good friends again after this arc.