Hello David,
Yes I too had wondered about that one and tentatively ruled it out. The following is a tad convoluted but here goes:
Three sisters are Sarah Ann & Mary STARBUCK
father is William STARBUCK
When Sarah married Francis SHELTON the witnesses are:
William STARBUCK [father]
Ann STARBUCK [next eldest sister]
Mary DODD [not sure as yet]
When Ann married Samuel MILLHOUSE the witnessses are:
Francis SHELTON [brother-in-law]
Mary STARBUCK [most likely sister]
Its the fact Francis SHELTON Ann's brother-in-law is a witness that lent me to see that this Mary was the third eldest girl in the family being a witness to the second eldest girl.
The second eldest girl was witness for the eldest girl.
So I saw the witnesses as a pattern and thus Mary STARBUCK was more likely to be the sister of Ann STARBUCK rather than a person from Harby. Interestingly some of the Harby STARBUCK's are related to the Harston STARBUCK's.
This doesn't mean that I am definitely correct in my hypothesis.
This is in part why I sought to look in the 1841 census where the STARBUCK siblings were living and if Mary was with anyone of her siblings.
I was unable to locate Philadelphia STARBUCK & her husband Samuel MILLHOUSE although based on other posts it seems Samuel is living at Grantham, Lincolnshire. The challenge is that there seems to be three differently named wives, Amelia, Philadelphia and Mary but only one Samuel MILLHOUSE.
Westy
