It's not a weird question, but I can see that it would be a bit hard to explain to her step-by-step if you have never had an ereader. The audiobook thing is out for the ereader - I think it would be too complicated for her to connect the ereader to the Show. However, she can play audiobooks from your Audible account if you have the show connected to your account.
I have two kindle ereaders I donated to elderly at my late grandmother's senior apartment house at the start of COVID lockdowns in March. One was a kindle keyboard and one a kindle Touch, so old ereaders. I just asked them what authors they enjoyed and loaded up 200 books on each ereader with whatever I had of those authors and related. I used
https://www.literature-map.com/ to help make more expansive selections. Fortunately, they preferred genres that I regularly read so there was no shortage of books. They do not have wifi access so adding books remotely isn't an option.
I did send books to my cousin's ereader remotely for 6 years. He worked in land management in Alaska and his only wifi access was a bar every few weeks. Once his ereader connected, Amazon downloaded the books that had accumulated. So I don't see this as a problem for your Mom.
As far as using the ereader, most regular readers of any age seem to 'get it' fairly quickly. If they've never used touch screens, takes a little getting used to, but not much. You can send books to her ereader, but I don't think you can delete remotely. There is a newish function on kindles that takes READ books out of the main queue. So, she won't have to have them in her way.
The most confusing thing is that selection bar where you select YOUR books or Documents, unread/read. Familiarize yourself with that so that you can explain it to her. Take photos of that screen popup so that you can follow along while explaining. Practice checking and unchecking and seeing results so when she has a problem, you might know to check those checkmarks.