Did I miss a signal she threw at me?

If you missed the signal, you haven't ruined your chances forever. She still likes you and you'll get another opportunity. If you're almost 100% sure she likes you, YOU can make the move next time you're together and not wait. If she feels like you might have been shooting her down, she may not be completely confident in making a move again so she may need you to take the reins this time. And if you're wrong, no big deal. Like you said, you're not giving much away - there's a 99% chance she already knows you like her. Why not make your move. If she mentions the open relationship, then say, "does that mean you'll say yes when I ask you out for dinner?". Or whatever. Or don't even wait for an opening. Next time you're talking to her, ask her out somewhere. You can do it - trust your instincts. You are probably right about her feelings and she'll probably be thrilled when you make a move.