According to the gravestone for Margaret and her husband John Beagle, Margaret was born on June 19, 1812. The 1855 New York State Census for the town of Walton, Delaware County, NY states that she was born in Otsego County, NY. According to the "Widow's Declaration for Pension" she signed on July 12, 1890 (for John's Civil War Service), she and John Beagle were married on May 27, 1836 in Worcester, Otsego County, NY by Rev. John Bangs.
With so much information, it looks like it would be really easy to find Margaret's parentage, doesn't it? Unfortunately, records for Otsego County are quite meager. Even a trip to the county courthouse and the historical society in Cooperstown, NY and to the Worcester Historical Society failed to give any clues. Census records are not very useful in the early 1800s because only the head of household is named and other people in the household may or may not be related to that person. I did check the 1810-1850 census records for Otsego County. The only Rifenburg who was in Worcester, Otsego County for the entire time frame was a Daniel Rifenburg. In 1820, there were two female children under the age of 16 in the household. In 1830 he still has a female child in the house between 15 and 20 years of age. In 1840 he is enumerated without children. This would seem to indicate that there was a good chance that Daniel was Margaret's father.
However, two factors come into play to question this connection. 1) In 1850 Daniel is 91 years old and his wife Christina is 84. His wife would have been 46 when Margaret was born. We do not know if Christina was Daniel's only wife. 2) A published family history written by her son-in-law states that Margaret's surname was Finkle.
So, was Margaret the natural daughter of Daniel? Or, was Margaret perhaps born a Finkle and adopted by the Rifenburgs? Hopefully, someday this mystery will be solved.