Violet is still King Riku's daughter.
And? All the Strawhats come from very different Backgrounds.
I doubt she will join the crew, because of that, and I think she despice being a pirate.
Hang on a minute.... HANG ON A MINUTE!
1. Zoro didn't want to be a pirate
2. Neither did Nami
3. Neither did Franky
She can perform the role of Look out ; assist Nami in navigation and be a dancer to go with Brooks music. She is strong enough to be in the mid quartet (as it will be when she joins), she also is female (like you said ; need more female members).
All Strawhats are based on and share similarities with characters and people from external fiction:
Luffy = Young Oda (Obsession over beetles and being rubber, Oda was obsessed with these two as a kid)
Zoro = Zorro and Francois L'ollonais (Name...)
Sanji = Leonard Dicaprio and Steve Buscemi (Hair, being a lover etc.)
Franky = Frankenstein (Pre skip he was also Popeye and Ace Ventura inspired...)
Robin = Cindarella (look at her childhood!)
Brook = A poem character (his story perfectly matches the poem)
Chopper = Rudolph (No explanation)
Nami = Cat Woman (No explanation)
Usopp = Boy who cried wolf (The story was also written by Aesopp)
Viola = Violet Gibson (Tried to assassinate Benito Mussolini, coincidentally she's headed to Doflamingos palace; most probably in an attempt to assassinate Doflamingo)
Other suggestions from the OP:
Sabo = Oliver Twist
Bartolomeo = Nobody
Bellamy = Nobody
Rebecca = Nobody
Toy Soldier = Nobody
Jinbe = Whales...
Anyone bolded has already been "disqualified" in the "contest" as Oda hasn't allowed them to follow the general trend. And Sabo wouldn't join Luffy if he is stronger than him. Ace didn't join so why would Sabo?