So, I feel like there are few things going on here. Your admin’s “workplace norm” is to overshare. She thinks that’s normal, and your boss not doing anything about it reinforces that it is okay. Starting from this premise, along with the fact that maybe she’s emailing you a lot of the time, I would (i) ignore it/just deal with it, (ii) tell her the same thing again to consolidate these non urgent requests (over the phone, not an email because tone can be tricky in emails), (iii) be a bit proactive and schedule a meeting for 10 minutes every day around lunch time to catch up, or (iv) take the burden upon yourself to do something about it so that it doesn’t annoy you so much. For example, if she’s just emailing you a bunch of non urgent stuff that you will deal with in due course, just not right now, I’d honestly set up a rule in outlook that emails from her go to a folder, and then I’d check that folder 3 or so times a day. If there was a particular case I was working on that I actually needed information on that was important, I’d add keyword exceptions so these ones made it through. This creates a burden on you, but depending on how much the situation annoys you, it might be worth it.
Also, does she get regular performance reviews? Who does these? In our office, my admin gets yearly reviews, and all of us attorneys submit evaluations, but they are delivered by our two office managers, not the attorneys, so the feedback is delivered in a more “neutral” setting than otherwise might have been. I’d make comments in these evaluations.
(I’ve done the last item when working with certain attorneys who think everything is a fire drill but it’s just not. I basically am muting these attorneys until I can deal with them and their requests. For me, it works, because if something is actually truly important and needs to be done NOW, they will call me. YMMV).