I'm so pleased to help. I found the proof of your Petra being Petra Albine and married to baker Peter Petersen.
Petra Albine's father Niels Peter Danielsen died in 1903 Femø Parish:
from the Probate Court (Fejø Birk Skifteprotokol) states that her father died on
September 3, 1903 leaving a widow and nine children. The youngest is 24 years
old. One of the children is staying in North America.
Next step was to find her mother's dead:
Dorthea Marie Danielsen, born Jørgensen died on May 22, 1912: Probate Court record
Next court record lists the children:
3. Petra Albine Petersen, f. Danielsen 12/1 [Jan
12,] 1866 gift med Bager [married to Baker]
Peter Petersen, 50 Aar gl, boende [living at] 2806
Bristol St. Omaha Nebraska, Nord Amerika