I had food poisining with my frist child it was a scary expierence I though I was loosing her only to find out I had food poisoning, I had eatten a chicken shawarma but the chicken hadnt been cooked well.
As for it being harmful its quite possible, I honestly would tell your sister to get checked by a dr, besides that if she is feeling better now I wouldnt worry too much just see a dr for your frame of mind
jess