Im not an expert, and with our sturdy red-headed sheep we dont have too many episodes of sickness really... but these are the questions I would ask myself.
The obvious first; has she been wormed? Has her diet been changed recently? Is she running a low grade fever? Is she coughing or wheezing at all? Does she have scours or loose stool?
When I cant put my finger on what the problem is, I throw the proverbial pharmacopoeia at them; I would worm first if that hadnt been done within the last 30 days; for lethargy, they get B Complex; cut back on any grains, go back to just hay; give her a good dose of LA 200 (if there is any respritory issue) or pennicilan; then treat the scours with some kind of microbial paste.
Without seeing the ewe, I really cant say what I would do in your shoes, but if you can answer the above questions, there may be a clearer answer in the waiting.

~~Becky

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