If you are going to write anything at all realistic about an academic's life, you first need to think about the subject. Doing a PhD in biochemistry is quite different from doing one in medieval history. In STEM there is often a lot of team work, in Humanities you may be quite alone. Like Witchend said you are not going to be able to write convincingly unless you can give a convincing picture of Helen's idea, the theories that underly it and the day to day work that involves.
As WeshMaGueule said, unlikely for a PhD to be properly groundbreaking. Though if you are in humanities, you may find, say, that yours is the only existing edition of an old text, so anyone coming after you may be forced to cite it whether it's brilliant or not. This is unlikely to lead to fame and fortune, though.
Someone aiming at a career in academe should also be getting teaching experience during your PhD.
The successful trajectory described- lecturership off the back of a PhD- is also getting more and more uncommon these days, with the growth of casual contracts. These days, unis tend to expect further publications and further teaching experience before they give someone a semi-permanent post. A good outcome would be a short-term post-doc and then (off the back of your second book) a lecturership).
As for following up Helen's brilliant idea, you first need to decide whether she is in academic employment or not. If so, she is probably (unless on a pure teaching contract) required to publish whether she likes it or not, so researching won't be about her confidence but about avoiding the sack. She also needs to be very aware of the dates of the next REF (national research evaluation) and plan her research accordingly: her department is going to be breathing down her neck about this.
If she is not in academic employment you are going to have to think about how she gets access to material and to ongoing academic discussions. If in STEM or Archaeology, this is probably going to be very difficult because of being shut out from lab access/researcg teams. More feasible in other branches of Humanities and what a lot of people have to do these days unless able to get post-docs straightaway.
And as Witchend said, a massive part of the job is going to be about chasing funding, and being rejected. A lot of academic life is about coping with rejection: you may have to rewrite part of your thesis, you will be applying for jobs you don't get, you will be turned down for funding, articles you submit will come back with requests for revision or simply be turned down. It's a life that consists of picking yourself up and trying again.
One of the things that always struck me as unrealistic in the Morse/Lewis films is how academics only seem to have One Idea and if anyone threatens that then we're in murder territory. If Helen has written a whole thesis and is setting out for an academic career she should have dozens of ideas. She may be terribly excited about one of them, but no modern academic can afford to be a one-trick-pony.