Not sure if this helps. A few years ago I interviewed for a senior role in the public service. I spent a few hundred quid on interview training which took place over three hours in an afternoon. A lot of the PR firms do it. (I got the job). I’m not sure whether the interviewee would be sufficiently resourced to afford such a course but they’re well worth it.
I’m not sure how senior the role is but the outfits that provide this service seem to have “inside knowledge” on how certain public service bodies conduct interviews and what they’re looking for in terms of experience and skills. And crucially how they score the candidates during the interview.
An obvious thing is to look at the job advert and match the candidate’s experience and skills to the competencies, as the interview scoring will be based on that. Make sure the candidate focuses on this during the interview. That and present well - CSO is public service so nothing too fancy dress-wise. “Conservative” dress is what I was advised. And all the usual stuff, firm handshake, eye contact etc.
Questions will largely flow from job description/ spec. I got a public sector job recently - video interview so I prepped all possible questions & had the Q/A's on post-its on my facing wall but behind the camera. It worked well. Not possible in traditional interview but was very helpful to keep me focused. Also google ' STAR' technique for answers.
I've given you a load of pointers there to work on.
Also have a good, convincing narrative about why candidate off long term. I was also in this boat (many years not working outside the home) for above and had my pitch prepared for the interview to turn it into a positive.
Given the long time since their last interview, and the current trend towards online interviewing, it would be really useful to have some sort of mock interview and other related training.
With the CSO, as with any public body, the emphasis will be on demonstration of the skills and attributes necessary to do the job.