The name did originally begin as a pet form of Sarah. However, it has long since been used as a totally indepedent name rather than a pet name.
― Anonymous User 6/23/2007
5
To a previous post, it definitely started out as a pet form of Sarah. It went out of style so it is very uncommon today and is now pretty much its own name but you will find a lot of older women who go by Sally are actually named Sarah.