Every few years, I get a few days of a mild case of flu or whatever and my body fights it off. Then, I seem to be immune to whatever everyone gets for the next few years. It's all in having a strong immune system and being sensible about potential for exposure, I suspect.
Best wishes to your niece and her family.
Unless it is an exotic strain with no human precedent. You have no antibodies to it. This is becoming increasingly common, but so far the strains haven't acquired the genetic material to zip around from human to human, or weren't that virulent.