Well okay then, that sounds promising. He bets she'll give that a go when she decides to turn. (His estimation puts it soonish but not immediately.)
Well! While he's here, can he help out in any way before he goes to report to his sister? Renovations with the house, maybe?
Soon enough, though, be bids the Cullens a fond farewell, and swims across the ocean back to his sister to report on progress.
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.
Carlisle's letter replies that deriving reliably usable information would certainly require test subjects eventually; the actual results might have to wait decades for the technology to catch up, but it's not impossible that careful experiments performed sooner than later could help. But she should certainly consider the possibility of simply - well, it's a letter, euphemism is the order of the day - keeping her options open in the traditional way.
Though, of course, she would need to know the specifics of the experiments in question before actually agreeing to them. Does he have an idea of what those experiments would involve, if he's willing to actually perform them?
(She assures him that she'll understand if the answer is 'no.')
She understands and will keep this in mind, and then asks if the diagnostics on their own would still potentially be useful, should she decide to not attempt to use reproductive tissue in this way.
Then she believes that it would be worth her time. Is he willing to conduct careful experiments?
She is perfectly happy to listen to his arguments, and in fact actively welcomes them, but believes that they would be better conducted in person. Would he mind if she and her brother visited?
Yvette has already been informed of the mind reader and is thinking thoughts along the lines of, "Yes I am okay with you reading my mind, at least for right now," while also sincerely trying to figure out potential arguments against becoming a vampire that could sway her, and coming up empty. And idly picking between places to be an isolated newborn in. She's a bit of a multitasker.
"Yvette, meet Carlisle, Esme, and Edward," says Blair. "Carlisle, Esme, and Edward, this is my sister, Yvette."
She thinks that they are very nice people, and also somewhat wryly thinks, Darn, there goes my dream to join you on a hunt and kill something with my bare hands to drink its blood.