Okay, so my partner is just recently divorced from his years-estranged wife. He does not know if he wants to get married again, but I do. In loving him and being loved by him I found the reason people would want to tie their lives so fully with another's. You are theirs and they are yours.
This bothered me for a long time, and I promise I'm coming to something (that I think might be) relevant to your situation.
I read a book.. where the crawdads sing? I'm pretty sure. Anyhow a line in the book rang true with me, "we are married like wolves and geese are married" and I love that so much.
So, while you cannot marry her in a legal sense, you can be romantic as fuck.
Also! Just thought of this while typing. Do a commitment ceremony, nothing legal obviously but maybe do a cool cultural marriage ceremony like jumping over a broom around a fire or any of the myriad other marriage ceremonies other cultures use.
Anyhow I'm sorry she's having a hard time and I wish you and yours (and theirs (= ) all the very best. I can imagine a poly relationship could be difficult at times but it sounds like you're doing all the right things.
Oh that sucks. Good luck to all y’all. Few states are worse to find yourself in than one where what’s normally exactly right for you is only almost when you’re stressed