Same person, different journal! I think I'll be using Debby Ryan and her first name is Mable. Adding to her 'star quality' (assuming it's okay by you) is the fact she was named after their father's mother. Naturally, this led to favoritism early on. Some last name suggestions I have include Murphy, Brennan, Walsh, Duffy, and Saunders. Nothing too unusual. And if none of them tickle your fancy, no worries.
I love the family details you've established already. Mabel (preferred to go by May) felt the weight on her shoulders to succeed where their parents didn't. The competition they tried interjecting between Mable and Branon was not okay, and once she got older and more outspoken, she tried letting them know that. I imagine talking sense into them is as impossible as shutting up your raging conservative uncle at Thanksgiving dinner?
She would have loved and supported his photography and wanted to go with him on shoots if only to get away from home for a while. Her method of rebellion against the strictness of their parents was dying her hair funky colors and getting multiple piercings. I would love, LOVE if they got matching tattoos on her 18th birthday.
I haven't decided what she was meant to study or what she really wanted to in her heart of hearts. But, my plan is to say that her brother and parents were led to believe she accepted a scholarship to a prestigious college prior to leaving on the trip. She did receive a scholarship ... but she didn't take it. The last call she made to Brandon was to admit that she's using the move as an opportunity to go to California and do [insert dreamy, unrealistic career ambition here]. She would have tried swearing him to secrecy because let's face it, she was kind of throwing away the opportunity of a lifetime.
Post-death, I would imagine it was kinder to let their folks go on believing she was college bound. Feel free to let me know your thoughts before I start working on her app!