I'd organise it for a day that suits DD and her friends. Family just need to fit it in, if they feel it is important then they will make the effort to come. There will come a point when she will just wants friends there anyway, not a party with all of the extended family.

I'm not inviting family members to anymore of DD's parties, it is just too hard to organise with everyone's varying schedules and travelling as all of my family are 2 hours away.