Corection: I thought your daughter was 5
My opinion stays the same. At 10, your daughter is still vulnerable. It sounds like she doesn't know who her birth mother is nor that she has a 1/2 sister.
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I suggest that introducing her birth family when the original plan was for her to not have contact changes the dynamics of your daughter's relationship with you and her forever family. The original plan was based on tge best interest for your daughter. You decide if setting up contact would be in the best interest of your child. Don't let the emotional appeal cloud your judgement.
If you are seriously considering this, which sounds like you are, I urge you to talk with a professional counselor who is very familiar with adoption issues before deciding.
adopted my daughter after being her foster mom. She came to live with me at age 6, nearly 7. So she knew her birth family. Contact with them upset her, in part, because contact increased her feelings of insecurety.. Once the adoption was final, at the recommendation of her counselor, I stopped visits from family members. It was a closed adoption.
I suggest that letting your daughter's birth family into her life will create big feelings that your daughter, even at 10, is not prepared to handle. As a teen, her birth sister, is already dealing with big feelings re her mother's death and now just learning she has a little sister. Teens are immature. I suggest that her mother should not have told her about her little sister. A healthier way for her to give her daughter the information would be to confide in a mature adult who could let her daughter know sometime in the future when it is appropriate.
This is an adult situation that should be navigated by adults. I would not let the teen talk with a 10 yo in this situation. As you said, your daughter is not equipped to deal with this negative and complex situation. She needs to feel secure in your home; to know that you are her parent. Contact with birth family will undoubtedly cause her to be confused about where she belongs. She will be more likely to question why she is adopted because she will have new and personal contact with her birth family.
Contact for the teen wI'll also be confusing. She just learned she has a little sister at the same time her mother is allegedly about to die. Consider how this rocks the teen's world. Just by reason of her age, she needs help with this. She needs support and will give your daughter more information than a 10 yo should have to process. MosT adults have difficulty understanding and dealing with emotions when they contact their birth family. Others do not want contact. I believe the decision to have contact should be decided by your daughter when she's an adult. Or by you when the decision us based on your daughter's needs instead of the birth family's needs.
Again, contact puts your daughter in an adult situation.
My daughter's brother was adopted by a family who had also adopted another child in a semi-open adoption. His adopted mom gave his birth mother information and pictures through the adoption agency. The birth mom had no direct contact with the adopted mom. She didn't know where they lived or their phone number. I hope your daughter's birth family has no direct info but it sounds like they do.
I suguest this birth mom is manipulating you by asking for direct contact with your daughter. An adoption means that the birth family gives up their right to be directly involved with your child. You make the decision about when your daughter IS. mature enough to gradually have contact.. GRADUALLY. The possible approaching death of her birth mother is not the time to get a 10 yo involved.
You have appropriately told her she is adopted at an early age. I believe this is all the information she needs now. To tell her more in this highly emotional situation.
I'd known and had some experience with adoptions before I became a foster mom. I adopted through the state who provided training and support in preparation for adoption. I saw first hand how difficult for both me and my daughter to be involved with birth family. Even tho the birth mother has released their child for adoption she often still feels an attachment. Having just learned she has a sister, the teen feels an attachment to your daughter. More so because she is losing her mother at the same time. I would say no to contact.
I'm sympathetic. At the same time, it's my responsibility to protect my daughter.
A later thought. Was the,adoption private through an attorney? If so, you perhaps did not get information regarding an adoptive child's need to be protected. There is an established reason for making adoptions closed or for having only the adults have limited contact. For the sake of your daughter, please get professional advice. Look at contact in an intellectual way without emotion.