Have you talked to her in person in depth about this issue? It is so easy to miscommunicate via text, online or even over the phone. Don't assume you know for sure what is going on until you talk with her.
There may also be some assumptions you are making that she is not and vice versa. There is nearly infinite ways to exploring same sex sexuality and they often share the same label of bisexual. It may not have occurred to her that you would want to develop a one on one romantic and sexual relationship with her as well as with her male partner. She may only want to explore being with a woman sexually in a group situation. She may not think of herself as capable of a romantic relationship with a woman - many bi women only want sexual contact but not emotional or romantic connections with another woman. She may be utterly confused about what she wants. Or she realized only after you brought up the possibility that what you offered is not what she wanted.
Your communications have been ambiguous (eye contact is lovely but difficult to pin absolute meanings to) and not very in depth. Hold off conclusions until you can talk in person, alone, for a while. I know that is hard.
And yes, you may not get what you want out of this relationship. Rejection is hard and no fun. (I have way more sympathy for men now after dating women.) Think about what you would want near and short term if she is definitely never ever going to be interested in a one on one sexual and romantic relationship with you. Maybe you take a break from group sex when she is involved. Do you want to be in a quad if that one on one relationship is not there with her? Start mulling over what you want, what you can tolerate, and how you see the relationships in your quad. Good luck!