Sounds pretty par for the course for a relationship that started out monogamous. She feels rejected because you established a relationship she was comfortable with letting her guard down in and you participated in for a good amount of time. So to her it looks like you took a good long sample of a relationship with her and are now finding it "not enough". Since she was the only partner you had in that relationship, she is having trouble not seeing it as SHE isn't good enough.
And once someone feels that way, it makes the transition to an open relationship even more painful. She's told you she doesn't want what you want but hasn't ended the relationship. She is probably hoping you'll change your mind and accept her as enough for you so she can feel good again. You still want what you want but have not ended your relationship. You're hoping she will get on board.
Maybe be a little more gentle since this is new to you too. Point out to her that if it was just about her not being enough you'd have broken up with her. But you haven't because you DO want her in your life.
Only other point of interest is you, in your 30s don't feel ready for marriage and babies. You may never feel ready. Does she want these things and does she want them soonish? You might still want her in your life romantically but the mismatch ideals with relationship style AND life goals might make it a cruel act to dangle her along expecting her to change for you.