Why do you keep ignoring the resemblances between Viola and Vivi? Both royals, both working under their enemies, and both being close to their fathers. You keep asking me to find connections, which I find a tad funny, 'cause the arc is not even over yet. Everything that turned Robin's character upside-down, happened in the last chapters of the arc. Something similar could easily happen again. Anyway, why don't you finally answer the question from my previous post and tell me: what connections does Viola have with Robin, that she doesn't already share with Vivi?
Robin did not in any way help the Strawhats, and if you think she did, then it certainly wasn't to stop Crocodile. It was out of curiosity, because of the initial 'D' in Luffy's name. Viola were in no way crucial to Doffy's plans, and, in the end, you try to overrate her position in the Donquixote family, but she was just a simple spy, with a convenient power. Nothing more. Even her betrayal was under completely different circumstances. The relationship between Robin and Crocodile was pure business, and there is simply no evidence that Crocodile mistreated or blackmailed her. He just kept his part of the deal, and she did hers, but, at the end of the day, she didn't want to give away Pluton's location. Their deal also supports my theory about Sugar's deal with Doflamingo.
They're not in the same boat, because she joined later on. It's the same with Viola as well, and just like her, there could be something more to her joining the Donquixote family. I'm not saying this means she'll join the Strawhats, but I still think it means there's more to her past with Doflamingo.