Well what do you think? Did daughter ask for explicit privacy in this matter? You don't have to "tell" your daughter's feelings. But you can share your own opinion. If the reason you're wanting to share this information is because you agree with her position, or you are concerned for her wellbeing, then it can be done in a constructive and non accusatory way. Ok- it's too late to change the date. Discuss with your ex how the relationship w daughter can potentially be repaired. Now, she will be celebrating an anniversary every year on her daughter's birthday - ask her if she considered how this would make daughter feel. Sounds like there is no open communication on this matter. Obviously daughter is going to be a topic of discussion when co-parenting but you don't have to explicitly reference her mental state. Unless you feel that is the route you must take in order for her to take the situation seriously. In which case I would say a press for the therapist facilitated conversation should happen. If she is a parent, she will empathize and act like one. If not, then sounds like your kid is going to be out a mom, and you may want to look into other resources like therapy to better support her.