Birthday card

Two out of three of my older children from my first marriage were physically abused by their stepdad KR so they want nothing to do with him or his family. Every year, his mother (who has been very vindictive since the divorce) sends my older children birthday cards. It upsets them and they throw them away. (My older children are 21, 20 and almost 15 so they know the abuse their younger siblings have endured and the cover up his grandparents have done for him) This summer my almost 15 year old said "I wish she would just stop doing this already.  Can I just send it back?" I told her sure. So she wrote ..."return to sender, leave me alone" on the envelope and sent it back, in hopes the cards would stop. A few months later, the younger kids came back from a visit. They were obviously upset. They said their grandma MR was visiting and had shown them a card she had sent to their sister that got sent back to her. She told them "your bitch mother sent it back to me and see what she wrote on it? She won't even let me send her birthday cards anymore." The kids said their dad was right there and also stated that I was a bitch for doing that to his mom. The kids had no idea that card existed before that day. The card had been sent to my parents home, and they were not with my older daughter the day she picked it up. So I know MR had really shown them the card.  I explained to the kids that I had not written that on the card, and that their older sister had made the choice,  and let their sister tell them that herself as well. I didn't let her tell them why she chose to. We just told them that MR was not her grandmother, she was their grandmother and she didn't want to have a relationship with her, end of story. The kids were satisfied.