You're doing something different and she's trying to figure out what's going on with you. For whatever reason she wants to be friendly and expects you to be friendly back.
Waiting a day to respond lets the emotional response wear off and lets you see the situation for what it is and respond accordingly.
Different people have different takes on maintaining conversation. The DB line is to treat the WAS like a neighbor, cordial but not overly friendly. If you go dark however that means no friendly chit chat, keeping communication to business only.
So responding about mutual friends makes sense. If your neighbor told you that other neighbors were expecting you would comment on that. But if your neighbor asked about D11 what would you say? If I were in that sitch I'd think that was a private family matter and wouldn't want to discuss it with the neighbors (but my mom would likely have told anyone who asked). Just think about it today and do not reply until tomorrow.
Here's how I viewed BF in my sitch: he was not treating me like a friend so he certainly did not deserve my friendship. He chose to be with OW so he no longer had any right to know what was going on in my life, good or bad. Simply none of his business. And the more I ignored him the more he wanted to know what was going on.
If you love somebody, set them free. http://tinyurl.com/2empx2g