Did you say you were ok with it or did you say that you really wanted her to participate? To me, if you say "I'm OK with this" it means you don't have a strong vote. Also if your D6 doesn't want to participate, does her vote matter? In my house a camp is an optional expense so if the kids don't want to go I don't force the issue.
As for how to resolve disagreements on childcare issues, I would think it would be the parent with primary custody. But if you aren't satisfied with how it's going, you can ask to clarify, or suggest co-parenting couseling.
Me42, H40 D12, S8, S7 A revealed: 7/13 Sep 4/14; Agreed to D 1/15