Ditto. Plenty of people do non-hierarchical poly. One way to handle it woulda be to have all three of you write out your ideal visions for what your relationships would look like now and down the road, see if there is any way those visions can agree. But really, her demand sounds immature. Why isn't bf just putting his foot down and saying no?
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.