If that's the case, I wouldn't mind dropping some letters in for you guys if you get them in before the end of the month? Otherwise, I was under the impression that fanletters were to be sent to the address below?
https://www.kronekodow.com/faq/faq0501.html
I'm not sure how many she herself actually reads, but Recohatsu was the result of a fanletter, so give it a go?
To approximate in English,
〒107-8583 Minato-ku Akasaka 8-5-30 UNIVERSAL MUSIC EMI Records Japan 「Sheena Ringo」
should get it to where you want it to go! the 〒 denotes the post number, but you don't need to include the 〒 mark, especially sending from overseas. It may confuse someone along the way to Japan.