Well, as far as I see it, if Koishi can read us, she'll already know that we have suspected her, whether we changed our minds or not. So I think it's too late to avoid that bit, now. Because until we find out for certain, one way or the other, I'm pretty sure we'll still have doubts in our heart, etc.
Anyway, here's what I had typed. Feel free to object, if you wish.
>"Hello, again, Kanako."
>"I'm sorry to come seeking a favor again so soon, but something has come up that I'm very concerned about. I managed to locate my friend, and... well... she doesn't seem herself, in a number of ways. She's organizing a giant fairy army to take over the Scarlet Devil Mansion, and seems convinced that this is a perfectly normal sort of thing to do, just because it interests her at the moment. She won't really listen to me."
>"I feel bad about suggesting this, considering that I have no proof, but... I'm concerned that Koshi may be involved with her, somehow. It's extremely circumstantial, but... you said that you spotted her in a very similar location earlier this morning, Renko spoke about a mysterious youkai who's been working with her, but who doesn't want to be identified or described to anyone else. She said she was a bit paranoid, she was also familiar with Orin. And Renko really doesn't seem herself."
>"You said that you can sometimes find her, if you try. Would you be willing to try for me? I want to be able to confirm or deny her involvement, and try to stop all of this before it goes too far."