Very much sounds to me like she's in a place of "OK, you had your fun playing about with this, but I'm done. It's poly or me, decide."
If that is in fact the case - pushing her, however gently, to reconsider will likely only make her dig in. Your watching shows about polyamory and trying to discuss/persuade her is going to make her feel pressured into doing something she's clearly not ready for, for whatever reason. I'd say your options are to drop it, at least for the time being, or risk losing her.