There's nothing about loyalty involved here, I'm not suggesting he's taken Riona to get her to work for him!
Okay, I'll change the wording slightly then - you hurt me, so I'm going to hurt you. It's about payback, revenge, not taking something as collatoral. Yes, money is a big thing, but power is another, and it's also important for a thug like Vinny to have the power and not allow someone like Quinn to take that from him. Taking Riona (to either hurt her, or just show that he can hurt her, and by "her" I mean anyone close to Quinn, or even Quinn herself) is a power play to teach Quinn a lesson. I'd be very surprised if it was just about trying to get money out of Quinn.