The incubation period for CP is 7-21 days post exposure. CP is contagious from 1-2 days prior to spots appearing until the last spot has scabbed over.
So, if the friend's DD wasn't exposed initially at the same time as her brother, she's now in the incubation period. You aren't contagious during that period, only in the contagious period (outlined above).
Unfortunately, it's obviously impossible to know if she'll get them and if so, when, so she could be contagious any time for the next 3 plus weeks.
Again as with your other friends' children, it's all entirely dependant on whether the initial friend's DD is now contagious or not. It's a horrible, vicious cycle with CP.
FWIW, my son was exposed directly to it (sharing food, which I never allow, but the other mother allowed them to share while I was out of the room) and didn't get it. I did however have him vaccinated within 5 days of exposure which is supposed assist to prevent or limit the severity of the dose (like you, we were going on holiday and I had a baby)
I know people will say that you shouldn't limit your life, but I would (and did!) as I really don't want my children catching it so you (mine are 2 and 7 months now).