This is confusing the issue.
Nobody ever needs backbow (nor can be achieved) for excellent string action from top to bottom of the board.
This process is simply to get the most opposing force possible from a previously maxxed out rod. The strings' own tensions will give you all the relief force you may need as you loosen the rod. Again: You don't need to de-tune when you loosen a truss rod. You only need to de-tune when tightening.
If your frets are finished correctly, your board should be about straight for optimum action. Relief is a graduated way to compromise for uneven or wearing (worn) frets or uneven fingerboard (Anyone not agreeing with this, check what Anthony Jackson and Fodera have to say on it. My basses are proof of it.).
The 180 flip may work for the basses she has with dual action rods, but I'm thinking that this may be more than she want's to tackle herself.
I think we're getting at the same thing, just using different terminology.
My question to her is, when set at zero tension, what does the neck look like?
That'll give us a great starting point.
Since she said she didn't have $$$ for any additional service such as a fret crowning, truss replacement, I really want to know what's going on with the neck.
When at zero tension and no string tension, what is the shape of the neck? And then what is the shape of the frets... meaning are there any frets that are visibly higher that those around them.
For me I have to eyeball this sort of thing. I take the strings completely off, loosen the truss all the way and look at the neck to see the shape. My experience is that my Euro basses seem to have some slight natural relief in this state whereas my USA models look to be completely flat.
On the backbow thing... if my USA necks are completely flat when at zero tension (string and truss) then the neck will develop some relief when the strings are tuned and brought under tension. Strings do that I think we can both agree. They exert enormous pressure on the neck and pull it forward (creating relief).
When I say I've got backbow on my USA basses, this is to counter the effect of the relief the string create when tuned... bringing the neck of my basses back to being flat again. Thus I'm able to get a 1/16th string height without buzzing.
But of course Stuart does the necks on every USA Spector and honestly the fret work on everyone I've ever owned or played has been the best I've seen. And I've seen some not so great fretwork come out of the Czech shop. My Alex bass has to my surprise some rough fret edges along the neck. It sort of surprised me. Ebony is harder to work with, but the fret work on my Alex looks like a rush job. Which I know it was because they were trying to get it to me for BPL.
So what I want to do in this situation is get a base-line idea of what the neck is doing. And from there unless the frets are shot or there's some serious uneven wear or they weren't crowned correctly (and I've seen this once or twice over the years)... I'd like to know because I think I can help her adjust the neck and get it playable.
Also, the height of the bridge saddles plays a lot into this. That's why I like to deal with one variable at a time. My neck adjustment/string height adjustment procedure is time-consuming, but I learned from Jimmy Eppard and I've yet to run across a Spector bass that I couldn't get the strings set to a satisfactory height.
I like your solution if we find the neck is bowed in a way it shouldn't be. Which can happen with all sorts of different environmental variables.
I like the idea of storing the basses in their cases, with some silicone moisture packs in the case if you find that your home/studio/whatever environment is too damp.
Here is LA I have the opposite. It's too dry. I have to keep my basses fingerboards oiled and I run a humidifier in my office so my books and guitars don't dry out.