Arianna was created because Rianna needed family. I would have asked someone to write her but I decided to write her myself as I wanted them to always be able to interact.
Arianna had a different upbringing, at first she had been adopted as a Darkligher, and was part of Corellian Intelligence, there was even a thought of making her an imperial at one point.
then in another place it turned her into a pickpocket. That was fun on the levels of Coruscant.
Each time she was taken home to Alderaan, brought into the family and became the heir to everything Organa since Rianna was a Jedi.
She's had a strange journey, and she continues to have one. I'd like to get her out more but all that I would have her do, her daughter Faith is doing.
Writing family members is easy its trusting your idea to others and letting them in to write members. You want them to see your idea and go with your vision. Sometimes that doesn't happen. I've given free reign to others in the past to write their characters if they wanted to make a family member, it has been wild.
At one time they went and got more Nohgri to use as guards, build up a military, started killing and conspiring against one another, it was fun. It's hard sometimes to find people who want to have fun, and don't turn the fun into something personal.
Ehh I'm rambling now..