I am not opposed to purchasing a costume and I did look for one. What I found was that the child costumes were likely on the small side for her and the adult ones were not really appropriate.
After looking at more genie costume images, I decided we could just make one.
Remembering flannel lined satin existed and might be warmer alternative gave us a starting place. I figured copying some pajama pants she had would make easy bottoms. I did have her try on a pair of my pjs to get a lower crotch length and we used that as a guide too.
The top gave me a bit of a headache. I wasn't sure how we should design it. Finally I settled on a peasant top. I looked at online patterns and used the pictures as a guide of what shape to cut. Then I made a top that wasn't right at all. After seeing where it needed to be bigger and contoured better, I tried again and it is acceptable. If I were to make another, I would probably alter things more and make the bottom lower.
After we had working pants and a top, we went to JoAnn's to get some trim. There were many options to choose from. The gold circles for the top were stitched along black elastic which made it easy to add. The gold trim for the pants had no stretch, so I was more careful adding it. I sewed along the top edge of the trim with gold colored thread. I intended to sew along the bottom too, but liked the way it stood out from the pants and decided to leave it sewn to just the top.
We did consider using some thin scarf like material to cover her midriff or around her hair, but decided against both.