Her mother had been the mistress of Ernst August, Elector of Hanover, who may have been her father. However, due to the promiscuity of her mother, her paternity can be ascribed to others as well. 
About twenty years of age she married Freiherr Johann Adolf von Kielmansegg but was also the mistress of George, the eldest son of Ernst August of Hanover. Her daughter, Mary Sophia born in 1695, was most probably George's daughter. 
When George, Elector of Hanover, succeeded to the British throne, he took two of his mistresses to England with him, Ehrengard Melusina von Schulenburg and Sophia Charlotte von Kielmansegg. Ehrengard Melusina became Duchess of Kendal and Sophie Charlotte Countess of Darlington. However, in England they became known as "the Elephant and the Maypole". 
Some people, including George I's daughter-in-law, were certain that Sophie Charlotte was the king's mistress despite her production of a certificate of fidelity, signed by her husband, but which failed 
to change anyone's opinions. 
Horace Walpole, who met her as a little boy, described her as: "Lady Darlington, whom I saw at my mother's in my infancy, and whom I remember by being terrified at her enormous figure, was as corpulent and ample as the Duchess of Kendal was long and emaciated. Two fierce black eyes, large and rolling beneath two lofty arched eyebrows, two acres of cheeks spread with crimson, an ocean of neck that overflowed and was not distinguished from the lower parts of her body, and no part restrained by stays---no wonder that a child dreaded such an ogress, and that the mob of London were highly diverted at the importation of so uncommon a seraglio!" 
However, both mistresses enlivened an otherwise dreary court without a queen. Sophie Charlotte was vivacious, moderately well read, friendly and eager to please; however, she was also rapacious and 
reputedly took bribes
 

Source: Leo van de Pas