This is the exact nature of Gigi and Greta's relationship... Greta loves her big sis and wants her to play with her all the time. It makes me smile that she is trading Skittles for love.
Greta frequently trades services or candy for some undivided Big Sister time and Gigi has usually put some type of escape clause into the agreement.
Gigi: "Greta if you do my chores I will play dress-up with you."
Greta: (Picture Greta quickly cleaning the bathroom sink and excitedly running to Gigi) "Okay Gigi, I did your chore. Now we can go play."
Gigi: "Not now Greta. I'm busy."
Greta: (in her whiniest voice) " Buuut you prooooomissssed!"
Gigi: "But I didn't say when I would play dress-up." (and exits the scene.)
At this point I usually sneak Greta a hug and a cookie.