Most eBook reader apps for Android will recognize file formats and make themselves default. For example, if I download an epub from ARe on my phone, and click on the downloaded file to open it, Aldiko automatically opens itself, and then opens the book.
Aldiko has "Files" as an option for getting books, and tapping that opion takes you to the folder structure of the device. You could make a folder with an obvious name (like Books Are Here, or something) to make it easy for your friend. Aldiko remembers which folder you opened and goes there immediately next time.
Once Aldiko has opened a book it automatically imports it though, and puts it on that shelf interface. The shelf can be changed to a list, similar to the Kindle apps list of books. It might be easier for your friend in the long run to get used to an interface based on metadata? That way she will be able to sort her books either by author or by title, and as her library grows, it will be easier for her to manage.
Aldiko screenshot behind the spoiler tag. The interface is very simple (at least I think so), and might be easier for your friend to learn than she thinks. The term "meta data" is scary. Call it "little labels" or something that makes more sense.
Aldiko screenshot, so you can see what I mean with getting books from "files". I was going to just post the picture, but it's kind of big and I'm too lazy to look up the rules about picure size right now.
