I feel like I shouldn't joke about this one as it might be more than a flu, so I won't write a joke comment. I sincerely hope that your niece gets better and I wish them strenght to fight biology against all odds. I know that your niece is loved, because you writing this comment means that they are in your thoughts, and that makes me happy.

Love them unconditionally and you will also give them strength to carry on and fight their body or external attacks against the body. The world throws shit at us every chance it gets, but your niece is a strong warrior who has survived until now. Support them, give them love, be there for them so they can build up their strenght when it's momentarily waining.