Elizabeth is interacting with ractors assigned (expensively) to the work, potentially at random although realistically that's likely to be why she ended up being recruited. Elizabeth's "failure" to use your word is that she ends up recruited into Cryptnet, about which we know nothing - we see one other individual in the story who is, supposedly a high level member of Cryptnet but denies all knowledge of it and his motives are unknown but seem perhaps good.
Fiona is interacting with her father, John Hackworth. The Primer's designer. That's what he's been doing for at least some of the time he was missing, he's her ractor, he's why Fiona's use of the Primer isn't costing much money. Fiona's "failure" is that she hooks up with Dramatis Personae, the outfit we see briefly whose true purpose is entirely unknown. Just as you might be disappointed mistakenly if you wanted your daughter to be a surgeon and she instead becomes a Nobel prize winning novelist, so Fiona's "failure" seems like a misunderstanding on your part.
Yes, Nell founds a new tribe (her Mouse Army), and is recognised by the Victorian Queen - which is perhaps a more immediately notable achievement, something likely to be written in history books, but lots of people do important things without appearing in history books. Her ractor, Miranda is her substitute mother (we're never told AFAIK what happens to Nell's actual mother, she's just written out) but while Miranda is important to Nell, there's no reason to think John is less important to Fiona.