Can I have German citizenship and U.S. if it’s reclamation?

Hi, I’m a U.S. citizen and I’m trying to figure out this whole process. My grandmother was a refugee to the U.S. from Nazi Germany (Hamburg). I have been looking into the process of applying for my German citizenship through their Jewish decedents application. I have all her immigration records, but not her birth certificate (where would I even find that if it still exists?) Does anyone have any experience with this? What should I know?

Thanks in advance!