This is difficult to answer. My guess, is that Eleanor Highfield was the daughter of Leonard Highfield, the Leonard who was the brother of Jeremiah and not Jeremiah's son Leonard. There seem to be 5 brothers that I have identified in that time period (Jonathan, Thomas, Leonard, Jeremiah, and Frederick), all born from about 1835 to 1850 or so. The parent was either Phillip Cropper Highfield or Benjamin Highfield. Since Benjamin had no children it is most likely Phillip Highfield. Only 2 of those 5 sons ended up in Kentucky (Jeremiah and Leonard) and it would seem that Eleanor was not a daughter of Jeremiah Highfield because his ancestry has been pretty well documented.
Notes on Leonard Highfield born abt 1747 St. Mary's Co,MD:
Fought in the Revolutionary War, private in the 12th battalion, Capt Henry Clarkson's company.
Calvery and St. Mary's Counties, Maryland, Revolutionary Patriots Listings, Page 139:
Highfield, Leonard, Private, St. Mary's county militia, 1777 (Ref: M-2101). "Leonard Highfield, farmer" moved from St. Clements to Pendleton County, KY in 1796 (Ref: X86)
1790 census, St. Mary's Co, MD: 3 males 16 and older, 2 males under 16, and 6 females.
There is a John Highfield listed in the 1800 census records in Pendleton Co, KY, possibly a son of Leonard?
There is a Susannah Highfield in St. Mary's Co who appears to be an orpahn 1/27/1816, she is mentioned in the archives records as need of support and the town of St. Mary's is commanded to provide support through a levy. She is possibly the daughter of one of Leonard's sons?
Leonard (abt. 1747) has sometimes been confused with the other Leonard Highfield, son of Jeremiah, but Leonard, born abt 1778, was too young to serve in the Rev War.
Eleanor was most likely the daughter of this Leonard because he was in the area at the time and was the right age to be her father. You probably have this information on John Miller but I will include it here:
Reported deaths in Nashville Christian Advocate:
JOHN MILLER born in Maryland, 1774; his father died in the Revolutionary War and his mother moved with her family to Virginia; he moved later to Mason Co., Ky.; married Eleanor Highfield; moved to Fleming Co., Ky. and to Platt Co., MO in 1842 where he died June 22, 1847 aged 72 years and 7 months old [September 1774].
1810 census, Fleming co, KY: John is listed with two boys and 2 girls and his wife. Next door is Robert Miller, with 4 boys, 3 girls and a wife.
1820 census, Fleming co, KY: John has 5 boys and 5 girls and a wife.
1840 census, Mason co, KY: John is living with 3 sons and 2 daughters and his wife.
Eleanor's sister, Sarah, born abt 1769, married Notley Duvall. Notley died sometime before 1850 because Sarah Duvall is living with her widowed sister Eleanor Miller in the 1850 Platte Co, MO census.
Have you ever been able to trace who John Miller's parents were?