Hello 'beachstreet',
When you sent your request for Cancellation to the buyer, did you first send any type of conciliatory note in advance? Without that, you could not seriously have expected the buyer to accept.
In my experience, people - both buyers and sellers - are not great readers. Your listing stated only Canada, US & Germany, but you did not actually exclude any others. She may not have noticed, and she may have bid at the last simply because that is generally the best way to win an auction.
Ever see one of those listings where they claim to ship worldwide but there are so many exclusions it almost seems they'd rather not sell at all? So yes, follow scifan's link and always select the many countries to whom you do not wish to ship.
At this point, however, you've got a bigger problem: she can leave feedback. That means you have 2 choices: You can accept payment and ship the item with a warm note of reassurance that the item will arrive but shipments to Brazil take inordinately long and hence your initial reluctance to ship to her country. (You hope for positive feedback).
Or you can refuse to ship, refund any money paid, and send a warm note of apology explaining that due to the exceedingly long delays by the Customs of her country you are unable to send the item. (You hope she does not leave negative).
So, -- get your listings set up, make a decision, and block her from doing this to you again:
http://pages.ebay.ca/help/sell/manage_bidders_ov.html#block
