Thanks all.
Squeasy - I shall be trekking through the snow again soon in that case and assume that even though she is showing no other signs yet, things maybe imminent. My sheep mentor didnt seem to have seen anything similar and seeing that she had little udder development said that if she did start it would probably be an abortion.
One of my favourite ewes lost her lamb last week. She had shown no signs of labour apart from being a little quiet first thing but then seemed as normal. Looked out to see her standing over a dead lamb! Nothing to be done. My neighbour came and checked her over and we were so upset not to have at least been there. Might not have been able to change the outcome but it is the what ifs. Probably being a little over zealous now and trying not to miss anything.