@Park -- My advice would be to ask her to work on dissecting her feelings and getting more comfortable, with the goal of giving you the same freedom you've given her within a broad timeline (4 months?). Its not necessarily reasonable, fair, or possible to ask her to get over her fear/jealousy/insecurity right away, but my perspective is that she should be putting in the emotional work necessary for you and the gf to eventually have the alone time and one-on-one connection that is (imho) essential for a serious relationship. Step one is figuring out why she feels this way. It will probably require some deep digging and long conversations.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.