Anna's Archive has basically everything, though it may take a few weeks for new releases to appear there. In that case, a private tracker like iptorrents is going to be where it's at.

Download Calibre on your computer. Once you have the book add it into Calibre.

Connect the Kobo to the computer. Once it connects, drag and drop the files over from the Calibre interface.

That's it!

The other option is using Calibre web instead, but that does take a little configuring. I'd consider my method above a good way "to add to her selection without making it more difficult."

Kubo = Kobo? Last I checked you can just put epub files in the ereader and it can read them. It's basically drag and drop files. Mine's a few years old but thats how it works. You can obtain epubs from wherever you like, though as an added tip if she likes reading from webnovels like I do, there are extensions for Firefox/chromium based browsers that let you pull chapters into a complete epub which is quite nice.

Use this to get annas books on mob.

https://github.com/warreth/OpenlibExtended

And install syncthing.

Install KOReader on Kobo and setup the syncthing plugin.

Now download a book and it will auto sync over.

You could to the sync with calibre or other apps. I just use what I know.

In my case I'm just accepting the slim pickings. Even with the pickings being so slim, I could still theoretically never run out of things to read.

That said the search functionality is abysmal and that's what's really giving me pause.

For my Kobo I've mostly used Anna's Archive and then converted epub from there into kepub format with Calibre; just need to rename the file to the epub file extension afterward (I usually keep both like My book.kepub.epub for my own reference).

Edit: MyAnonaMouse is indeed a great community as others have said though I found their selection to not be as good though that might be biased to the topics I prefer to read.

A nice community, a lot of shared books.

Here is a working Libgen link.

Install Calibre on your computer.

Go to Anna's Archive or Libgen to find and download .epub files. Use Open Slum to find an online instance.

I personally have a setup using calibre-web-automated and koreader to store books on a server (laptop I put Linux on) and send them to the ereader with opds, but that's a whole thing to set up.

Simplest way I can think of is get an epub off of Anna's archive or zlibrary, connect the kobo to the computer with USB, move the epub to the device. Shows up no problem.

Assuming you mean Koboassuming you mean Kobo, Grimmory has a good system. I haven't found a good way to automatically get books though, so typically I browse Anna's Archive or Z-Library