We had one last year with a grapefruit sticking out whenever she lay down, which started a couple of days before lambing. The worst bit of it was that I gave her an energy boost drench (badly

) which then made her cough, and each time she did......
In the end, she lambed normally, but then had an infection and a very smelly rear end. This cleared up with ABs and a pessary from the vet. Our vet was pretty relaxed about all of this, and said if she was his, he'd give her another year.
However, I think I'm going to follow your lead, Marches Farmer and give her Calciject as a precautionary measure (it's only a fiver a bottle after all). Another month until we know if the vet was right or not!