The only Sidsel Maria I could find from Ringsted is christened Apr. 12th 1781 in Ringsted.
The 1787 census shows her father as a widow:
Soroe, Ringsted, Ringsted Købstad, Ringsted, Nørregaden 94
Joergen Mouritsen, 43, Widow, Shoemaker
Jens, 9, Son
Sidse Maria, 7, Daughter
The mother obviously died between 1781 and 1787.
The (possible) parents were married Nov. 20th 1777 in Ringsted:
Shoemaker Joergen Mouritsen and Wilhelmina Dorothea Larsdatter, both born in Ringsted.
The surname Blanck doesn’t show here.
It will take a little more effort to find out if this is the right Sidsel Marie, and from where the name Blanck enters the scene. However, the name is present in Ringsted at that time (a carpenter Just Blanch, born ca. 1728, is in the 1787 census).