I have assumed that Sarah was the daughter of Thomas Plucknett and Elizabeth Loaring but I have not succeeded in finding a baptism. However, a copy of the will of Thomas Plucknett, the text of which is shown on http://jonvic42.wordpress.com/2009/03/09/the-faces-of-history-thomas-plucknetts-will-1860 indicates that Sarah Loaring Coombe was his daughter.

More information about the Coombe family can be found on another page of that website: http://jonvic42.wordpress.com/2008/12/18/the-faces-of-history-thomas-loaring-plucknett.