Thanks everyone! Just got home from work and I'm tired, so I'll make a better post later.
By biblical I was referring to, God doesn't say "No poly, only monogamy." It's nowhere in the Scriptures. That's where she's having the hard time. Church always preaches monogamy, etc., but the teachings don't come from the Bible. The church is the one who mandated monogamy way back when as a means for economical resource. The men just couldn't support more than one wife and the children that they would have. So, the church stepped in and said "monogamy only". Yes, there were certain cultures that were monogamous, but it wasn't a generalized practice until the economy got strained.
The only reason I talked Bible with her, was because that's immediately where she took it. I didn't even ask her about joining us. I just presented it as a conversational topic that we are chewing on for ourselves, so I could get a feel for how she was taking it. As soon as she cut me off last night, she text me husband saying, "Don't call or text me tonight." He asked, "Just tonight or ever?" "I'm not sure yet."