In a nutshell, if she's not okay with a polyamorous relationship, she needs to figure out how to get okay with it.
The only alternative as I see it is to go back to being friends without the sexual/romantic component.
You were open about your nature all along. She really has no right to get involved in a polyamorous person, then later decide she's not okay with a polyamorous relationship, and expect you to be the one to make the changes.
I suggest asking her to read Tristan Taormino's Opening Up
. It will give her insight into your feelings. Wouldn't hurt for you to read it, either.