Hehe. You're very welcome ^^. I have more ridiculous bondage stories than I'd like to admit. ><
But you can do it! Ask her questions to help draw out what she wants/needs and to find her limits and likes. Something like *twists clothespinned nipple* 'do you like that?' works fine. You can think of dominating like a puzzle or game: what do I need to do to solve this problem where this uppity sub will not say 'Please, Mistress.' Which buttons do I need to push and in what order?
Just dig deep and find confidence in something for Nadia that she can warp and apply to this situation. Maybe just confidence in that she's the only one wearing clothes and therefore isn't vulnerable? So if Jamie giggles at her bumbling attempts, so what! Nadia's the one wearing clothes and Jamie's the one that's naked, cold, and tied up like a helpless fool with a clothespin on her nipple. Or take confidence in the fact that she has all the parts Jamie wants and she will be unable to resist Nadia if she keeps teasing her. The confidence that your sub won't be able to resist you is what makes domination work for me.
And you don't have to use force or pain to dominate, seduction and manipulation work just as well. Nadia's a dancer, make some seducing with her body happen ^^. I'm sure Jamie will agree to whatever the hell she wants if you dangle a pair of nice breasts just slightly out of reach. Think of dominating her more like teasing a puppy dog. You're just trying to get her to want to play so bad that she whines and whimpers and will Sit, stay, do whatever, if it just means you'll throw the damn ball and let her play.
Easy stuff! You can do it! =D