The moment you completed the naturlization process (12/12/12/) is the moment you're daughter became a USC. Even if she doesn't have a US Passport, she still is a USC by law.
We almost went through the same thing, that's why we went to a passport agency instead of a post office. Main advantage is you could have picked up her passport within a day or two and they deal on a daily basis with the child citizenship act. You can read why here:
http://www.visajourney.com/forums/topic/431566-our-story-crba-for-our-child-denied-entering-the-us-with-a-baby-transportation-letter-and-citizenship-through-the-cca/
"Receiving US Citizenship under the Child Citizenship Act of 2000 and a US Passport"
As long as she was under the age of 18, and in your legal and physical custody, and a permanent resident when you became a citizen, she became eligible to receive a US passport. Therefore it doesn't matter if the passport was applied for before or after her 18th birthday.
If you want additional proof of her citizenship status, she may file the N-600 application - she is now over 18 so she should be the one to fill it out. The date on the certificate should be the date when the parent became a citizen.
I recently went through a similar situation.
My wife had her naturalization on May 28th. Her daughter (my stepdaughter) fulfilled all the requirements of Section 320 of the Child Citizenship Act of 2000. Both of them applied for their passports at the Seattle Passport Agency. My wife had no problems with her passport application. She submitted her Certificate of Naturalization. However, the agent denied her daughter a passport. We submitted 1) her mother's Certificate of Naturalization, 2) her foreign birth certificate and 3) proof of permanent residence...her green card. Still, the agent requested more evidence. School records, baptismal certificate. Of course, we didn't have those documents (as this was not specified in the DS-11 instructions). He stated that if we couldn't furnish any of those documents, we would need to have her own Certificate of Citizenship or have a maternal dna test performed.
Of course, I know that the agent is misinformed. I quoted Section 320 of the CCA of 2000. He still insisted on providing additional evidence. We did plan on have her own Certificate of Citizenship. However, we'll get our state representatives involved in expediting her N-600 application. Since there is no biometrics or civics exam (for minors), we hope to have her certificate issued ASAP. It really irritates me that one person's ignorance of the law will cause so much inconvenience to others.
Right! The date on the Certificate of Citizenship should be the date the parent naturalized.
