IMO, the safest route in gifts would be something that was about the kids. There are all types of jewelery with birthstones, etc., but that might be too much for the WAW. She would feel pressure about wearing it.
Maybe a beautiful picture of your children in a picture fame that has their names engraved.
When it has something to do with her children and nothing about you & her, she'll be more receptive.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!
