if Finn suffers from kidney failure, Li will do anything in her power to get ready for surgery. But for that, she'll need a donor. And unfortunately, no one other than Sheila Carter will be fit for being Finn's savior.
Li and Jack Finnegan don't match Finn's blood type. And you can't just search for a person with the same blood type to donate a kidney for you. That will only make it harder for Li to cover up.
Hayes Finnegan being Finn's son might be compatible but he's still a very young child. That leaves us to Sheila Carter.