I think (in my own lil warped mind) that not responding would send that message as well.
My criteria - if it involved Peanut and was something I needed to respond to (i.e. I will be dropping her off at 630 instead of 6, or Peanut forgot a coat - when can we come by to get one because I am too lazy or cheap to buy her one for here) not (How was your day? or I can't believe how much Peanut has grown.)
You have to find your own benchmarks and set your own limits though. Eventually you will come to a spot where you realize her intentions and you'll decide what is "worthy" of your response. You taking time out of your day to respond to willy nilly BS...will one day perhaps be a thing of the past.
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....Understand, that I can't, not be what I am I'm not the milk, and Cheerios in your spoon ~ Avril Lavigne ~ ..."Nobody's Fool"...