I would tell Jay that you've ben thinking more about poly and that it occurred to you to wonder how she would feel if you approached this woman. If she's not comfortable with it because of your past history with her you can either let it go or press for why it would be ok. But I don't see why you couldn't just ask Jay what she'd think. If you two can come to a good place about it, then you can reach out to the woman and see what she thinks. And then maybe, just maybe, dating! Doesn't seem all that complicated.
The major players. Me, 30ish bi female. Gia, girlfriend of 4+ years. Clay, boyfriend/dom. Davis, ex/friend/"it's complicated." Eddie, roommate & fwb.
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. Liam, Eddie's husband.