Sean,
I'm sorry to hear about this situation. I will say that unless you two are literally attached at the hip, you didn't completely make her go back to rehab. She always had the choice of just not doing it and saying "Well Sean will have to deal with it or leave." But she did not, and that's a sign that she loves you and deep down knows that it's for the best.
Is she as religious as you are? If she is, I wouldn't use this as a tool to keep her in-line. If you were to say things to her about how oxys are sinful and taking them is committing sins, it would probably just make her feel bad for sinning and want to do more to escape those bad feelings. You can remind her that Christ loves her and is there supporting her as she gets through rehab, sure.
And on that note, to yourself - Forgive the sinner, not the sin. If you want to keep your family together, you need to forgive her for lying to you (or probably more so "witholding information"). Even if she's not showing much remorse yet. Drugs make people act different from how they typically would. My guess is that if she does complete rehab and stays clean, she'll apologise to you or something similar.
Just keep your attitude and outlook up, and take care of your son. Be there for your wife, but don't be too pressuring. Give her the benefit of the doubt here and now.
I hope it all works out for you, her and your family!
