N.H.
I once had to stay home b/c my sister was sick. I was not but b/c she couldn't go on the trip, I couldn't either. I still cannot, to this day, fathom the 'why' in that decision. It's not her fault that her brother is sick so on one hand you should allow her to go. Although on the other hand, she has been exposed to whatever is making him sick. Could she possibly 'spread' the illness to others at the park although she isn't physically sick just yet, she could 'carry' the illness w/her. It's a catch 22 but if she's still well when it's time to leave, then perhaps she could be allowed to go. Good luck!