A land mine certainly. Say nothing. If the fact that your daughter in law never says thank you for a gift, then stop giving the gift. So many of the letters to Dave Eddie are about how another persons behaviour affects or bothers the letter writer. The simple truth of the matter is we are not usually going to change a persons behaviour by saying something to them. We usually  only end up damaging the relationship. What we need to learn to do, is to accept people for who they are. If their behaviours and actions bother or affect us, then we need to look inward and change how we react to the person. Only then will we be happy. Life is far too short to allow the actions of others to affect us so deeply. Deep breath. Forgive. Move forward.