heck don't sit down & shut up, your thread is one of my favorites, I think we've all learned alot from it, and I look forward to the book and I expect a book.
Your response to her when she crossed that boundary was emotional, that's not how to respond, I would have told her that she needs to put a lid on it and respect you when she's around you & the kids, she needs to keep her personal life to herself.
Getting up and leaving or storming out as it sounds, was kind of like, I can't stand to hear this, it hurts too much, i need to get out of here right now. If anything I would have asked her to leave if she continues to talk like that, give her the choice to smarten up or take a hike.
If she says "what's the big deal", tell her that you could easily talk about "Miss Someone" when she's around but you don't need to flaunt it, your self-esteem is intact and don't need to brag about your fun and it's kind of sad for you to see her continuing to reassure her weak self-esteem and deflated ego at your expense - it's boring.
She has poor self-esteem, I can guarantee you that. No one who is secure with themselves would need to flaunt what they're doing as much, it's the only thing that she feels makes her feel like she has value & self-worth but she ends up looking like a joke. People who feel better about themselves by attempting to make others around them feel worse have low self-esteem, they only feel better when they make someone else feel worse.
Knowing this gives you an advantage and actually gives you a bit of insight into her world, she's insecure, very insecure.