Welcome to our forum.
The others have kind of already stated my take on your dilemma, especially opalescent who proffered what I thought was quite an apt metaphor.
I think your main problem here is, not your wife's lack of involvement, but your own struggle with guilt. What's at the root of that guilt? Is there some social conditioning you're running up against? Try to analyze your own psychology a little (in light of the points that have already been made in this thread). Is your wife really pining away for you at home? What's really going on here?
Your marriage is important and you should always give it your best. Make sure your wife doesn't feel neglected. But think of this: It makes sense to believe her when she says she's okay with your poly activities. Do you doubt her at her word? It almost sounds like you're trying to get her to attend various poly events as a sort of way of "getting evidence" that she's really as on board as she says she is. But I would submit to you that she's responsible for her own honesty, and that your part in that bargain is to believe what she says.
So if she says she's happy in the marriage, she's okay with your poly stuff, and she's not interested in her getting personally involved ... believe her. If she comes to find that she feels differently later on, she can let you know at that time. But it's not very useful to try to cross that bridge before you get to it, especially since you may never get to that bridge at all.
From your description, she sounds like an easygoing, generous, open-minded person who can handle your poly nature (without having to get involved). Don't let your panic button get the best of you! Things are probably fine.
For what it's worth, hope it helps,
Love means never having to say, "Put down that meat cleaver!"