I don't know whether you have resolved this after all this time but there are 3 Sarah Edwards in the Llanferres baptisms c1809.
6 Dec 1807 daughter of David and Mary EDWARDS
5 May 1810 daughter of Edward and Jane EDWARDS
12 Aug 1810 daughter of John and Mary EDWARDS
There is an unamed EDWARDS 18 Sep 1809 child of Robert and Catherine EDWARDS
Hope this helps in some way NellieT