Answer 1 inject her now and then again in 4-6wks time this will get her in line or inject when you do the new lambs and pre lambing next year . Answer 2 no any age Answer 3 If i read it correctly, to give the new born lambs the best cover 4 wks before birth is good , but since you can't know exactly when they will lamb you have to do a best guess. If you raddled your ram and recorded the service dates then you will have a fairly good idea of lambing dates, you can ask your scanner, if you use one for potential lambing dates