Oh, goodness, if there is one thing sheep are good at it is confusing the shepherd about when they will lamb!
Yours does sound like she's getting close, but as to when exactly ... well, we have had nine deliveries so far this year and only witnessed one, and that was by total fluke (we happened to be looking out the window at the time!). The one that gave lots of clues was moseying around the pasture, nosing at the ground, pawing, picking a spot to lay down, getting up, moving, bossing someone else out of THEIR spot, and generally being cranky. She delivered her lamb in the 10 minutes between 'window checks', literally!
If you really want to be sure, put her in a pen in the barn (got a barn? not all of us do...) and use a baby monitor. The mamas make this very different snuffling sound at their babies, and at least you'll hear if she has already delivered ... and if she is in pain/trouble she will grind her teeth and you'll hear that. Looking and watching just doesn't seem to work (for us, anyway) unless you camp out in the pasture.
Best of luck!