Oda basically used her as a cheap plot point to get the roger pirates and non xebec rocks pirates there. That's it.
Again, call it cheap or whatever; objectively, Ray got what everyone else was chasing. Have you ever thought the great WB would say something like, ".....if she falls in love with me, well, I am not complaining......."? Roger was disgustingly shameless about Shakky. Lets not act like these guys were your average Joes.
You have to look at it from Oda's perspective. Give Ray a flashy AdCoC move? Screw that, I have already given him iconic moments like being Luffy's haki mentor, stalling Kizaru, humiliating Blackbeard, etc. This time I give him something better, the prize Roger, WB, and everyone else were after.