I would think that if she's started then whether or not it's an sbv or normal lamb there would be physical signs, water bag or just fluid leaking, I had a ewe this year who was very uncomfortable for a week before she lambed, breathing was heavy, and she stared a lot, she also laid down flat, stretched out, she was on the verge of twin lamb disease, fortunately liquid life aid saved the day. Sounds like shes on her way and maybe things are getting moving?