I think in PA it is 18 but I will check into it. I'm very open with her and she could see her birth mother now if she wanted to and we could actually locate her. She met her three siblings last year and now keeps in touch with them. My adopted son (now 20 years old) has no interest in meeting with his bio mom or siblings but I've always been open with him and left him know it was an option.
In MO, where I live the legal age of adulthood is 17. Some states it is 17, some 18. If I were you I would check into that. If legal age in your state is 17, I would just wait a few months and do an adult adoption. Then you would not need anyone's consent other than yours, your husband's and your (now adult) daughter. Then you could complete your adoption without stirring up a hornets nest, although if your daughter is interested in meeting her birthparents....this would be the perfect opportunity to make that happen.
You still have to find both parents (or make every attempt to locate them) in order to do TPR. Once TPR is completed by the court, then you can begin adoption process. If you can't locate the birthparent, you have to show valid attempts at really trying to locate them. A judge won't TPR because you said you can't find them. You have to SHOW PROOF that you really tried - for example, by contacting motor vehicles to get address, putting notices in newspapers, sending certified mail to all known addresses..etc. If a judge isn't 100% convinced that you did everything possible short of going door to door in the state, he will not TPR. He'll tell you to hire a private investigator to find the parents. There is no way to adopt a child without the birthparents finding out about it. You have to locate that birthmother & get her consent or prove that you went through great lengths to locate her. Once she is found, they will try to find out who the birthdad is-and then probably have you post a notice in the newspaper and check the putative father's registry to make sure he has been notified of the adoption. Once you have birthparents consent OR a judge agrees that you made a 100% effort to locate the birthparents & signs TPR, THEN you can file your paperwork to adopt. You can't do it without birthparents consent.
Now if you wish to go it alone, there are ways to do so. One such way is to utilize the services of a Do-it-yourself adoption service such as RapidAdoption.com. For a reasonable fee, the fine folks at RapidAdoption.com will complete all of the necessary paperwork for the adoption in your state. They will even do it if the child is in a different state than you. They have been doing legal paperwork since 1998 and have prepared 1000’s of legal documents in all 50 states. But their service is only available in the United States and only with domestic adoptions. So if you reside outside of the United States or are adopting from another country, then this is not an option for you.