I think it's important to keep some distinction between things from a philosophical perspective as well as a practical perspective.
I think we all live somewhat in one or the other of those worlds at different times. With our unique personalities one may have one foot deeper in one world than the other more of the time.
And in regards to poly, relationships etc, this is VERY much a factor. There's a definite philosophy that you either gravitate to or not. It sounds like you both do.
Then there's the practical side. Different beast.
Getting too wrapped up in either living or pursuing 'poly' can be time and emotionally draining. Different people have different demands on them in their daily lives and some are (even if temporarily) tapped out on either or both ! So the desire just isn't there.
We've both been on and off this wagon more times than I can count LOL
Maybe this is where you two are at right now. She may just have a lot going on in her life (and head) and as much as she might be philosophically comfortable with the whole idea, just simply doesn't have the resources left to put towards it.
Be patient. Relax. Time changes everything.