If I was confident that it would make a difference, I'd send a letter or e-mail in a heartbeat; I'm ok with admitting this in a forum with people who share my feelings on the matter: I genuinely care about the welfare of artists I admire. Unfortunately, I don't think it's a good idea for me to do so.
Although people who are far more knowledgable than I am have put some very solid and thoughtful ideas out here, but it's still strictly speaking speculation until Wakana herself or her PR state otherwise. I don't doubt you guys at all, but an overseas fan asking about something like this might seem...odd. 'Out-of-turn' might be the best phrase to use here?
I guess I'm not comfortable in discussing a very sensitive subject with someone who doesn't share my first language - the chance of misunderstandings, and additional upset/distress that may result, are too high: when there's a language barrier there's also a risk of genuine concern coming across as criticism or worse. If we're right and she's suffering from health issues, the last thing I'd want is poor Wakana being worried about fans criticising her on top of everything else, just because some well-intentioned statement is 'lost in translation'.
In short: as frustrating as it is, I'm going to have to wait for official confirmation. At that point it would be perfectly all right to make public shows of concern and support that won't be misconstrued as something else.
Just out of interest, has anyone seen similar threads to this one on Japanese-language discussion boards? I know this is probably in a bit of a niche, but I'd expect 2ch to be all over a story like this (given the reputation it has for occasionally tactless, unsympathetic fans though, maybe it's for the best that this hasn't happened).