So, first, do NOT frame this up as whether you are "qualified" or have sufficient experience. That is the death knell to a career, because it says you don't have confidence in your work or your abilities. If you start getting that reputation, everyone will start to look twice at the work you are doing *now* in your technical role (not joking, not exaggerating -- seen it happen, to people who were actually more competent than I was).
In addition, women (assuming based on username) tend to undersell their own competence -- you seem to be a perfect case in point, where you clearly have several years' of knowledge and expertise but want to make sure every box is checked before you risk taking on more. It is the job of a good boss to evaluate her employees and decide when they are capable of more -- my boss here did that and routinely pushed me into issues long before I myself thought I was capable. Turns out he had a much better perspective on what the job actually required than I did.
If you admire and respect your boss and think she is on the ball, then trust her judgment about your ability to fill the new role. You really, really, really do not need to know 95% of everything to do the job (or else no one would ever get promoted) -- they key is to have resources on your team to fill your own knowledge gaps. Which, conveniently, goes along with the "delegating" skill others referred to. FWIW, I took on a new role here @4 years ago that was in an area I know zero about -- I think I got it because I was mouthy to the person who had it before me (which, since the role requires a backbone, turned out to be a plus). I was totally *not* qualified substantively -- I would quiz myself whenever a new issue came in, and for at least the first six months my gut answer was consistently wrong. BUT I was allowed to put together a team, which I compiled from the subject-matter experts in each area. So while I threw myself in to learning the area, my experts kept us on the straight and narrow -- and, added bonus, even after I figured out the basics, I *still* don't have to know all of the ins and outs of each little sub-area, because, duh, that's what my experts are for. You really truly do NOT need to know everything to be a good manager (in fact, it can be a detriment, since that entices you to do everything yourself) -- you just need to know enough to lead the team and keep everything honest.
OTOH, if you don't want the promotion because you don't want to be a manager, that is a completely valid reason not to go for the promotion! My DH has a Ph.D in a technical field, loves the tech part of the job, and has spent the last @5+ years babysitting a couple hundred people instead of developing the tech -- he is now looking to lateral to a CTO-type role to spend more time on the tech and less on keeping the trains running on time and resolving interpersonal disputes.
But the key to pursuing that kind of role is exactly the advice you received above: you need to keep the discussion positive and focus on what you can contribute in a "senior technical person" role, rather on "I don't want to work that hard" or "I don't think I'm ready." It sounds like that may be difficult, because you have a project-based job, and your existing projects are winding up. But try to think creatively about a role that you can propose that shows you are still passionate about the work and want to work hard for your company. It sounds like your company has a clearly-defined organizational structure, but also that they have had a tremendous amount of change lately. So that may mean that there are options they haven't considered -- if you can find an area that is underserved, some need that is going unmet, you could propose yourself as the "boss" of that particular issue/area.