Hi there. I can tell that you're a bit flustered by this. First thing I would do is sit down with her and ask her what she means by "polyamory" and how she sees it in her life. The thing is, poly isn't necessarily about not being in a committed relationship. It just means you can be in more than one committed relationship. So, is that how she put it, or how you interpreted it?
There are so many ways to be non-monogamous. It could be that what she thinks she wants isn't poly, or that what you thought was supposed to be poly in your previous marriage wasn't managed well enough or maybe wasn't even really poly, either. You both just need to talk about what it means if you did agree to poly, how you would proceed, and how it would affect the kids. You definitely should tell her how it was for you in your previous poly experience.
Read threads here, ask questions, and invite her to join and post also. This is a big step. I started a recent thread about how to prepare for it and there are some interesting ideas people have shared. Here: Prepping for poly - how?
But there are tons more here about opening up an existing relationship, if you search around.