I'm with Purv on this one. Better to say things now rather than later; it may be more of an issue if we leave it. And it won't make us look any better if we start hiding stuff from Kanako. I mean, she helps us and trusts us; no point in breaking that by hiding it, even if it is a big thing. Actually, more of a reason there.
Plus, she'd probably give help more than she would panic. That is, of course, not to say she won't.