As Charlie says, and definitely yes to a dose of antiBs. Flystrike will knock them back badly, leaving them exposed to other infections such as pneumonia.
I can only think that the Crovect missed the bit which has been struck, or possibly she was so close-shorn that there was no wool for the liquid to stick to. Bad luck, but well spotted. One of the ewes we rescued had been badly struck but now she is doing really well and the wool is beginning to regrow over the whole affected area, so no scar.