They don't sound familiar, but I may know names of possible parents. At least now I have a rough idea when she was born. Will go through all my McVickers and see if I can see potential parents for her.
My Vollmers could be part of your Vollmer line, but in 1919 or so they were in MN or WI, then in the 1920s they moved down to CO. As far as I know they weren't in St. Louis MO. Vollmer sounds like a German name, so I am not surprised that they emigrated from Germany.
Here is my Zeigler data, it doesn't sound like they match your PA Zeiglers:
Susanna Zeigler (b. 1750? VA ; d. GA) + Joshua Tillery (from VA ; d. GA) =
Judith Tillery (b. 1780 NC ; d. TX) + David Callaway (b. 1779 NC ; m. 1800 ; d. TX) =
James Wilson Callaway (b. 1816 GA ; d. TX) + Caroline Elizabeth Dillard (b. 1829 TN ; d. TX)
I am interested in a Henry Jacob Vollmer, who was married to Stella Theresa Harris. They had one naturally born son, who was a Catholic priest, and they adopted a daughter named Dorothy Marie, who was born in 1914 in Minnesota.