But the other recipients of the Primer both do something it's just that this novel isn't about them, indeed maybe the point is that their paths diverge so enormously. Princess Nell is exactly what Nell intended from the get go. We don't see Elizabeth and Fiona's first interactions with the Primer, it seems safe to assume they do not begin by escaping from a terrible castle since their lives are comfortable and there's nothing to escape from.

To the reader perhaps it seems like Fiona doesn't amount to anything, but we're not shown very much about it, and it may well be that to her this is every bit as much what she wanted out of life as Princess Nell's outcome. All we know about Elizabeth is that she joins CryptNet. The novel never even tells us (beyond hints) what CryptNet is about. It tells us what CryptNet claims to be doing, and it tells us that nobody believes that.

You could read it as the other two girls fail, but I'd argue that from what Elizabeth's grandfather says at the start, and what the Constable tells Nell later, we can see that the grown-ups have a sense that actually conforming to somebody else's expectations is exactly what they don't see as a path to success. All the parents want what parents so often want - younger copies of themselves, but that's stupid. Nell isn't what Tequila (or Bud) wanted, Fiona isn't what Hackworth wanted, and Elizabeth plainly isn't what her mother and father seem determined to make of her, which suits her grandfather down to the ground.