Anonymous wrote:How old is she?
I'm coming from the perspective of an adoptive parent. My opinion is that it's best to bring it up casually, before they're old enough to make sense. The goal with a really young kid isn't that they "get it", it's that when they're older and you are ready for real conversations with the details, they'll be like "oh, I've heard that word before" and they won't feel like anything was hidden, or shameful.
+1 - and make sure to get the whole story out by the time they are 12