According to ComicBookMovie.com on Oct. 6, "Doctor Who's" Karen Gillan spoke of her role as Nebula in James Gunn's "Guardians of the Galaxy". Apparently, since the initial comic book literature portrayed her as someone without hair, then it would stand to reason she'd be hairless in the film as well.
"She’s bald in the novels, Zoe’s character has hair. So their look was predefined and my hair had to go".
That being said, Gillan has to keep her cue ball head shaven on a daily basis. Gillan also gives a revelation with the nature of the relationship that she has with The Mad Titan Thanos and Gamora as played by Zoe Saldana.
“Not very much I can reveal, I’m afraid. It’s all very hush-hush. But I do have a lot of sibling rivalry with Zoe's Gamora".
For those not familiar with the kind of history Gamora has with Thanos, but she is actually is his adopted daughter that was raised in a manipulative manner until she reached a point where she saw no good in his evil deeds and flees his accompaniment.
Also, in the comic book world, it is claimed that Nebula is actually Thanos' grandchild. In the recent issues with "Thanos Rises" in the Marvel comic book limited series, he apparently had quite a few lovers, all by which he had slain to appease his only true love Lady Death.
So one could understand the drama and possible sibling rivalry as well as daddy/grand daddy issues.
To see this sibling rivalry and sarcasm in its full array of surprises, go see "Guardians of the Galaxy" on Aug. 1, 2014.