OCD notwithstanding, you must be satisfied that an appropriate (not excessive) amount of daily pleasant interaction with your daughter is fine. Interaction with her peers, friends and other adults should round out her social development.
I would respond to her whining by saying something like," When you want to talk about this and not whine, I'll be in the other room." Then leave her presence. Hold your ground and don't let her get you frazzled; that's one of the goals of this negative behavior. That and perhaps drawing your attention away from her less demanding brother.
Take a look at Faber and Mazlish's book, Siblings Without Rivalry. They give many examples of how to empathize with your daughter's conflicted feelings towards her brother while letting her know how special she is.