Since you say that the other 6 sheep are looking fine then I would have thought no reason to re treat them . It is your vets advice to re treat the poorly sheep so ok , it could be that this ewe was already suffering liver damage before you treated her in which case even with a retreatment with a totally different product it is still going take a long time for her too recover . You could ask your vet for a syringe of B12 this stimulates appetite and try her with some ivy . Did the vet have any theory as to why she is licking the bricks , salt ?