You could go Kindle Fire HD 7" or 8.9" and get a simple, media friendly tablet. While your memory is not expandable you can go with Netflix, Amazon Instant Video, or Hulu + to satisfy video needs. Spotify for Music needs and the Kindle marketplace for any books. Also the interface is fairly straightforward and simplistic so she (shouldn't) be asking you questions about how to do something 24/7. Personally I like the 8.9" simply for the 1900x1200 resolution but that's just me.
I guess what I should ask is if you're looking for expandability exclusively, if so then a Kindle Fire won't float your boat. Perhaps the Acer Iconia A200