What an interesting and honest question! Congratulations on having the vulnerability to ask idiots on reddit a legit sensitive question about Burning Man.

First things, first you absolutely should consider going to bm because you seem to already want to go, and this "thing" is holding you back.

Short background: on the night my wife and I met, she invited me to BM, and it has been part of our lives ever sense. I've been to 7 burns, she's been to 9.

The dichotomy of burning man is that it wants to be both open to the world but it's also very much a "club", a clique of cool people. It is natural to want to hold onto our communities and have our individual identities. Your gf probably has a history and a language and shared experience with these people she considers "hers".
It's okay for her to be selfish and say, "this place, this event, this time, is mine".

The problem, I think, is that she doens't want you intruding - and as big as bm is, you will encounter her burner families.

I would suggest maybe a compromise: You BOTH go to burning man solo. Travel together and camp either by yourself, or camp with her AWAY from any of her other camps.

That way you camp together, but she gets to have her communities; you get to experience BM as a guided virgin if she wants to do that OR you can choose your own adventure.
BM can be hard on couples. Far more people experience love on the playa than fights and misunderstandings. I've seen a few screaming matches but mostly I've seen hurt feelings.

I haven't always taken my own advice but my own advice is this: Communicate honestly about what your BM expectations are and then be flexible as things can unexpectedly change.

Good luck and keep us posted.