I'm trying to set up my Kobo for my mother. If she doesn't like it, she'll give it back but if she does like it I am prepared to let her keep it---she is about to retire and I think she'll enjoy it

Obviously I plan to pre-load it with some books for her, and she seems excited about it (it took some initial convincing, but now that she's on board, she is excited) but she is a bit worried about what will happen once she is done with the books I pre-load.
She is not very computer-savvy. I can see her figuring out the Kobo software, but I think she will want to borrow library books too and I can't see her enjoying having to juggle multiple software programs. And I don't see what the Kobo software really adds to the experience unless there is something obvious I am missing---I used ADE (actually, the Sony software) just fine before the Kobo software came out, including with my test unit which didn't have the software on it.
Come to think of it, why not just use the Sony software? Then she could buy with Kobo, Sony OR the library...
I want to set up ONE program on her computer, teach her how to use it and be confident she is good to go. Best plan?