Isabell and her elder sister Hope, like their parents, were slaves of Nathaniel Sylvester at Sylvester Manor in Shelter Island.

Isabell was given to Grizzel's 14 year old daughter Elizabeth Sylvester.  Nathaniel Sylvester's Last Will and Testament 1680.  When Elizabeth married in 1686, she moved to Southhold and Isabel went with her. 

This meant that Isabell  was separated from her family  and went to live in Southhold with Elizabeth.  Unless Elizabeth was visiting Shelter Island, Isabel may not have been able to see her family again for years.

The 1698-1700 Southhold Census showed Hope living on Shelter Island, but Elizabeth Sylvester and Isabell are listed on the Southampton Census.

Isabell's sister Hope was  bequeathed to Grizzell Sylvester , and probably lived and died on Shelter Island.

Additional reading is available at Sylvester Manor : https://www.sylvestermanor.org/slavery-at-the-manor/hannah-jacquero-hope-isabell/

More research necessary.