I'm a bit late in coming to the "do I respond or not to her posting", but I wouldn't address the issue w/her again. How many times have you told her that you would not consider a relationship w/3 in the mix? She's not listening to you. She is doing what children do, they cry, they whine and beg until mommy and daddy give in to shut them up. She knows how to play the game to wear you down. The only way that you will get through to her is by your actions.
If you've not sent a response, then don't. The more you try to rationalize w/her and share your thoughts/feelings on the subject, the more she knows that she's got you still on the hook. Step away from her drama. You do not need to explain yourself again. You've already done this at least 2, if not more times in the last few weeks.
Actions speak louder than words.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
