I did a deep dive regarding this and what I learned is you have to be very careful not to paint the real-life characters and companies in a bad light. You also have to add a disclaimer at the beginning of the story stating that it's fiction. I'll definitely be doing that if I decide to publish the entire story as a book. What kind of fan fiction was your niece into? You're right, most people associate a younger person staring at a phone with social media or games.