It seems that she is in a defensive frame of mind. Having been in a place myself where I was caught up with NRE and also caught in an ailing marriage, I know too well how the NRE-infected spouse can feel. Of course, in my case, this happened at a time when I was rebelling against everything. I learned to regret the way I neglected my wife, but at the time, sometimes I almost had the perspective that she was the enemy.
Your wife will probably eventually come around, and feel bad about the amount of pushing she's done. This is a stage she's going through and if it's at all like the one I went through, she's probably suffering within her soul more than she has a "right" to. The natural thing to think is that she should be having a great time in life, having *two* guys with her husband's permission. The reality, though, is that she is probably in a place of inner turmoil. Not everything about NRE is fun and roses; it is also a source of intense yearning that can stretch one's heart and compress it against the walls of the impossible. If you have any compassion to spare for W, I would guess that she probably needs it.
I do recognize that you have pushed yourself way beyond the bounds of social norms in order to be accepting of this foreign relationship situation. W is not extending the compassion to *you* that you deserve. The best you can hope for here is an opportunity to set the better example, to be on her team even if she seemingly won't be on yours.
You've been very generous towards her. Sometimes giving a lot leads to a state of resentment or keeping score. You give a lot and W barely seems to give any. Try not to hold that against her. Polyamory.com is a good place to vent so do take advantage of that resource, but let the venting be an act of letting go if you can.
I hope the surprise party will help her understand that you are on her side. It would be a shame if she felt defensive and guilty about it, though that's an unfortunate possibility. It would go against the purpose of a birthday celebration, which is to bring some happiness to the person whose birthday it is. I hope she won't let her fragile state of mind interfere with that.
You deserve kudos for the patience you've already shown, in any case. I have hope that it will be worth it in the end.
Love means never having to say, "Put down that meat cleaver!"