Need Advice from Birth moms

Here is my story: I adopted a sibling group of 4 last year. THey were all 1month to 4 years old. Their Bmom or Bdad never visited them before their rights were terminated. The Bfather relinguished his rights and we had an agreement that I would send pictures of the children and later he decided he did not want them. My issue or problem is actually with the Bmother...... She never went to court...she would not show up. When my baby was 3 weeks old she left him outside in a parking lot at 10:30 at night and a man later found him. She was convicted of a crime due to abandoning her son. Since the adoption of my 4 children she had another baby in August which I now have. She relinguished her rights and we have an agreement only with the new baby that I would send her pictures and letters. Here is my problem. She took the agreement so she could write to the other children and not the baby. I sent her a letter stating that I could not keep any letters she wrote to the children unless she included the new baby in her letters. I told her that I had to look out for the best interest of all my children. She responded in a letter stating that the baby was "different" from the other 4. She said she loved the 4 but not the baby. She said she didn't love the father of the baby and loved the father of the 4 and therefore did not love the baby. She said she wants pictures of all the kids except the baby. Our agreement is only with the baby reguarding pictures. I know she loves the kids except for the baby and it hurts me so much....how could she not love her. Here is my question.....What do I do? Do I keep the letters eventhough the baby is never mentioned? And if I keep them what would I tell my baby when she is older about why her mother never mentioned her?I want to do the right thing. I am a christian and want to do the right thing for the Bmom and the children. They have a new life but 20 years from now I don't want to have any regrets.