When there is such an obvious gap in ability it isn't always possible to have whole group activities nor is it healthy for everyone. Yes there are things they can do that can include eveyone but each age group also deserves to do things that challenge them and have the right to do it without interruption from the babies etc. The child is the diva princess of the castle at home would be my guess and she needs to learn that to have a friend one needs to act like a friend. Then work on what that means, not taking toys, asking to join in not demanding, sharing, taking turns etc. Let her play on her own if she abuses the group privileges and don't feel guilty about it. It will take a certain amount of isolation for her to realize she is bored, sad, alone, etc. When she is ready to change then you can help her. When the big kids are gone the play level will return to a more even playing field it sounds like. Try to set up duplicates of some things so they can be doing the same thing but in different nearby areas so two bins of dolls, dishes, etc in case you need to quickly separate them and don't know who to take away from the centre - means they can both play in the centre just on opposite sides of a shelf or table or something with their own stuff - parallel play vice cooperative play which is really the stage she is still at.