I see that Claire is pretty blinded by... her desire to live. She's bound for death anyways, so I think it would have made more sense for her to want to kill Erin just so that Claire isn't the only one to suffer, not because she can go back to living a life of luxury. Then again, she's not very bright. She would have continued to live a decent life if she wasn't greedy, but we can see that both the prince and her are cut from the same cloth. Greed will only consume and ruin you in the end (in these stories, anyways).
But I don't know how they would make it so that Erin enters the carriage alone... That's just a really lame, convenient plot point if it's not Rowan noticing someone's point and letting them attempt the assassination to take down the offending culprits.