The most important thing to know about Estelle? She's Emoto Hed's daughter. That's like saying she's a gangster's or Mussolini's daughter. Wouldn't you be a bit scared of her? You'd think she's probably something like her dad, right? Well, yes and no.
Emoto Hed seems to be known throughout the galaxy for being one bad mother, and his daughter doesn't seem far off. Well, obviously. She learned it from him:
Her first few thousand years had been spent in her own quiet campaign to get the measure of her father without inciting his easily incited wrath. She had learned a great deal from their relationship. A great deal about sidestepping danger, about subtle maneuvering and oblique angles. She had learned the uses of persuasion, of silence, of a steady gaze; had learned to hold her nerve and not back down—without presenting herself as a challenge. She had learned, occasionally, to be sneaky. (23.2)
So this is a tricky lady. A smart lady who can wriggle herself out of any problem that she gets into—which is how she solves nearly all the problems in the novel with one fell swoop. For most of the first part of the novel we get this idea of Estelle as cold, quiet, and calculating. Sort of like Wednesday from the Addams Family.
But underneath that quiet polite exterior we keep getting the image that she's the kind of person that we shouldn't make angry. For example, "Estelle's smile, small and amused, nonetheless had the power to turn blood to ice" (31.40). That sounds pretty creepy, and we're thinking we should take it literally.
Or what about this: "She had made up her mind long ago that the family business was not for her, for she was quite certain that she did not share her father's ruthless streak (though in this, she was substantially mistaken)" (41.29). Yep. Scary.
Since soooo much is made about how beautiful Lucy is, it's noteworthy that Estelle is described as not beautiful. Bob calls her "Miss Plainy-Pants" (28.4), and not even Mr. B calls her beautiful. Not that he thinks she's ugly. He describes her this way: "With her long straight nose, pale skin and high forehead, the girl might have walked straight out of an early Renaissance painting. Not at all weaselly. She was slim and graceful; she moved without flapping or fuss." (28.12) Maybe she looks like this?
We don't know, that sounds pretty beautiful to us. That leads us to think that "beautiful" in this context has something to do with sexuality and femininity. Lucy is totally sexy. The main goal of half the novel is to have sex with her, and her body is described as a totally traditionally feminine shape.
But she is also not the quickest on the draw. She's not dumb, but we get the sense that she's just a pretty average girl. Estelle, on the other hand is cold, kind of scary, and she's got a razor sharp brain. Even though Lucy complains about people judging her based on appearances, Rosoff uses appearances to make a clear difference between these two main ladies.
Just like Mr. B is Bob's opposite, Estelle is Lucy's. Luckily for them, their relationship works out a lot better. (It might have something to do with the fact that they're both immortals.)
See, underneath it, Estelle does have a good heart—along with that ruthless streak. Just like Lucy, she loves animals—particularly the Eck. With the Eck, she becomes nurturing and loving:
Estelle has been a vigilant nurse. She is there when he blinks open his eyes and there again when he recovers enough to feel thirst. […] Estelle holds him in her arms. His nose lies against the outside of her left breast and across her armpit, curling over her shoulder in a soft hook. She smells to him like linen and teacakes. Hour after hour she lulls him to sleep and lulls him awake again. (43.1)
Well, gee, that sounds nice. We couldn't really imagine the Estelle from before that chilled people's blood with her smile taking care of anyone like that, let alone a measly little Eck. This transformation turns Estelle into a perfect partner for Mr. B, who is the other character who cares about other people's suffering. Beta couples for the win!