After reading about your WAW, I suspect that there is probably a little passive aggressiveness going on. However, maybe not. I would send her a quick note thanking her for the thoughtful gesture. That way she doesn't get to think that she upset you, and you don't say anything else that looks like pursuit.
No no no no. Do not respond at all. Thank your kids the next time your see them, but do not acknowledge anything to your WAW.
