Ordering Shiratama Hime:

Maki-san accepts Internation Postal Money Orders. If you don't know what these are, they're very easy to get. You simply go to your post office and ask for one.
You tell the cashier you want an International Postal Money Order, to what country, and the amount. That's all there is to it.

She doesn't speak English, so information has to be sent to her with some Japanese. This means your computer will need to be able to at the very least read Japanese.

In Japanese, she needs to know which books you want. 白玉姫 is the title of her series. Last I checked, 6, 7, 8, 11, 12, 14, 15 and 16 are available.

She sends the books via EMS. Shipping overseas is expensive; be prepared for that. It can easily cost as much as the books themselves do. If you bought all of the books, you'd probably be paying about $25 for shipping. Of course, only one book would cost a lot less. When you order from her, she will give you a dollar amount based on how much it costs in yen (1 dollar is actually a little more than 100 yen, but most people divide by 100 to get a quick idea of what they'll pay).
The books themselves only cost a couple hundred yen.

You'll need this information:
郵便番号（ZIP code）
住所（Address）
国（Country）
氏名（name）

Here's a sample e-mail you might send.

Mailto: kananmaki@yahoo.co.jp
拝啓、
日本語が全く話せません。白玉姫15,16を注文したいのですが。
(Insert country)に住んでいます。国際郵便為替で支払い可能ですか?

郵便番号（ZIP code）
住所（Address）
国（Country）
氏名（name）

お時間を取っていただきありがとうございました。

~Name.

Essentially the translation of this is:
Greetings,

I can't speak any Japanese. I'm sorry. I'd like to order Shiratama Hime 15 and 16.
I live in (insert country). Can you accept International Postal Money Orders?

郵便番号（ZIP code）
住所（Address）
国（Country）
氏名（name）
Thank you for your time.

~Name.

Some countries have different International Postal Money Orders that might not necessarily be accepted, so it's good to ask.