If the cat normally doesn't wander far from the shed - perhaps you could build an enclosure; a high wire fence with wire "ceiling", high enough for a person to walk to the door of the shed, with a door of its own.

Or you might have to enclose all around the shed.

Or - live trap her and try to make her an indoor cat...how tame is she?

Your vet might have some ideas as well. She is defending her territory, and I don't think that can be trained out of her.