Your morbid friend has been reading a good book on Typhoid Mary. If you're not familiar with what happened to her, she infected 22 people in various households killing one, was quarantined by the state for two years, promised never to cook again, was released, started cooking again, infected twenty five more people killing two, then was quarantined for the rest of her life.
Her whole life, she denied that she had the disease.
I'm realizing that I haven't a clue what, had I been there, I would have advocated doing about this highly contagious woman. She seems like Dostoyevsky's proverbial baby getting tortured at the edge of the universe so everyone else can be OK.
Locking her up on an island for the rest of her life doesn't seem like a solution that I should be OK with, but I can't think of anything else that seems like a reasonable solution either.