Thanks so much for your reply. I really appreciate the time you're taking to help me. I went through my mother's adoption papers yesterday and discovered Berta's address in Frankfurt in 1946, the year my mother was adopted. I found a picture of the house on google-earth and showed it to my mother. She is fairly certain it's the same house she went to in 1958 where the sister/her aunt opened the door. I wrote a letter this morning to that address explaining the situation and my hope that if any Haller's are still living there that they will write me back or email me. I'll give this a few weeks, if I don't hear back, I will write to the 20+ Haller's in the Frankfurt phone book. There are also about 40 Haller's that live in Frankfurt that are on Facebook that I can message. If none of that brings answers then I will write to Frankfurt vital records again and ask if they can find any records on Berta Haller's siblings or the child she had 2-3 years prior to having my mother.
Is there a link the "Meldepflicht" you mentioned? I googled it, but so many things came up it was confusing and in German. Once I find a good website I have a translation site I can use but finding the right website is always difficult.
My mother and I are traveling to Germany in June 2014 to visit her (adopted) sister. My hope is while we are there we can travel to Frankfurt and meet with any living biological relatives she may have. I hope 8 months is enough time to find these people, if they exist.
Thanks again for any advice you have. It's sincerely appreciated.