I would get a small bottle with a spray nozzle on the top, fill it with water and when he goes near her just spray him. It won't hurt him and he won't know it's come from you.
Sometimes my young cat Harley gets a bit rough with my 2 fifteen year old cats and that's what i do. He just runs off.
Other than that you could put her in another room for a couple of days so she can rest up. It's cold and damp now and probably won't want to go out.
I think if we were poorly and somebody was stressing us out we would want to be on our own for a bit.
Hope she will feel better soon.

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