Moments

Eden: "I want to get my princess dress and play with the light on in my room"
me: "You can get your princess dress and play in here in the sunroom."
Eden: (throwing a fit) "I don't wanna play in the sunroom!!"
me: "You can play in your room if you want to, but be kind to Arielle"

A few minutes later Arielle comes back into the sunroom, whining, trying to get away from Eden with Eden following close behind.  Arielle finds a spot to sit and enjoy the toys she's brought with her and Eden starts to hover.

me: "Please leave Arielle alone and let her play while you go back in your room to play princess."
Eden: (throwing a fit) "I wanna stay in the SUNROOM!!"
me: "Not to long ago, you stood right over there and threw a fit saying you did not want to play in the sunroom."  I re-enact her moment from earlier.
"Now, you are sitting right there throwing a fit to stay in the sunroom"  I re-enact the recent fit.
Eden: (covering her ears) "You are too loud, Mommy!  I don't like that."
me: "Oh, really? 'cause I'm just being Eden.  Look at me, I'm Eden."  I start whining again.
Eden smiles slightly.

Unfortunately, although I thought this was a bit of a breakthrough moment. The same ol' plague of desiring only the opposite of what I request and desiring only what the sibling is playing with has continued throughout the morning and I think it's time to break the cycle by going somewhere.