His sister is not thrilled, but also not particularly surprised. She requests an address to send Carlisle mail with, gets it, and then Carlisle gets a letter.

She identifies herself as Blair's sister, and mentions that he's spoken a lot about Carlisle and his family and she's heard only good things about them. She dutifully does not mention vampires in it at all, but what she does do is ask if anything helpful could be learned from a willing human subject that would theoretically be losing the option anyway, and therefore can afford to be a test subject. To potentially save someone else from this particular issue.