Welcome to the world of Hebs!
I can't tell whereabouts on the body that lump is. If it's just generally somewhere, then have a close-up look to see if it is a sheep tick, although it looks too big. Ticks have a head and legs near the front (hard to see when it's bloated), and can be twisted out using a cheap tool from the chemist. Don't pull them out as that leaves the head buried, which can cause an abscess. That might be what has happened - your shearer may have chopped off the tick, leaving the head behind, and that would turn into an abscess. If it is, don't prod at it, but spray with something lemony (you can make a spray yourself with a lemon chopped and boiled in water, peel and all) which helps to keep the flies off. Check around for eggs or maggots.
Equally it could be an abscess caused by a nick from the shears that you didn't notice. Or it could be a sign of CLA, especially if it is on the side of the neck. Caseous LymphAdenitis. That requires a vet to view it and treat it. Some lesions there are also caused by injecting Heptavac - they may or may not become infected. If it was a pre-existing abscess of that nature, then being cut by the shearer could have opened it which would attract flies. CLA can be spread by shears, especially from a travelling shearer who isn't totally hygienic with his shears between farms.
If you are really worried, then pop her down to the vet (cheaper than paying for a call-out) for a definitive diagnosis - we really cannot tell just what it is from a photo.