At last we know what's wrong with Kristina...
It's rheumatic fever. "Although the disease seldom occurs [especially in the U.S. -- which is no doubt why it took so long for our American doctor to figure out what it was], it is serious and has a mortality rate of 2-5%." At least, if you can trust Wikipedia.
Kinya's specialist strongly suspects that it was heart damage due to rheumatic fever that killed Lyena (Anya's and Kinya's older sister, who died of heart failure at 13). Now, there's no reason for it to get Kinya as well anytime soon, especially since (a) we now know what's happening and (b) she has access to the American health care system, which the Obamessiah has not yet had time to turn into the Canadian health care system or into the British NHS. But it does mean that for at least the next five years, Kinya's going to have to get penicillin shot into her butt once a month.
I would have preferred for it to have been mononucleosis, of course. But at least now we know, and we can start actually doing something about it.