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.