Oh, I wouldn't blame her insecurity. There are plenty of ragingly insecure poly people. And I might be reading you wrong but it seems you've portrayed or at least insinuated that polyamory and commitment are mutually exclusive. I disagree. It's definitely possible to have strong commitments that don't include exclusivity. A current relationship I'm in has a stronger emotional connection and more clearly defined commitment than any relationship I've been in previously, including the monogamous ones, and I honestly feel it's because we're trying to act the way that polyamory idealizes, and not just sexually.
I didn't mean to imply that, more that I found it easier to learn how to manage jealousy when starting on a less committed track. I now think I can carry those skills over into a relationship, if I want. It was compared to my earlier approach of essentially jumping into a committed relationship with no practice at non-monogamy and not being jealous. I view casual dating as a great way to try - to dabble at - polyamory and practice shedding jealousy. As opposed to starting out with something that feels very intense and serious and having that be your first go at not being jealous and/or practicing polyamory.