My first instinct is one you may not like. She is straight, likes you, may have fantasies of women but is in the end still straight. If you do eventually have sex with her, you may not appreciate the aftermath. A lot of bi-cuious people walk away from who they got to play with because of discomfort. What throws up flags for me
1 - her demand to have the man in the room, almost as if she is trying to be turned on, or continue to justify her straightness by having the man in the room, like a straight safety blanket.
2 - her husbands well..everything. In you want a poly relationship with her, you have to work with him. He is homophobic and clearly doesn't get poly. By getting involved with her, you may REALLY rock their boat
My wife and I have been through..similarish situations. We were open long before we were poly, we found a few girls that wanted to try being bi, but ended up straight. We found them at the right time, they were willing to play and give it a go. You seem to have patience, but it may be a while before she is ready to just dive in
“The love between a man and a woman is very sacred…it is not as good as the love between the same sex.”
In its own way, this is quoted by every man who is willing to let their wives have sex with women but not men. It might not be this bold or in your face, but I think this is believed more than you think, and by apparently progressive people too.
Best of luck on your journey, I am sure more people will comment. Maybe someone will understand this all too closely. But if my wife and I were in this situation, I would be trying to convince her to keep her close as a friend and step back, leave the door open of course, but to back away and give some room.