What's the weather like with you? She could be hot! All that fleece and lambs to carry... If it is warm, then if you do bring her in, make sure there's plenty of ventilation. Indoors or out, does she have access to plenty of fresh cool water?
Is she fit and active apart from the panting? If she's unsteady on her feet, reluctant to move, anything like that, I might be suspicious of twin lamb disease and at the very least give her a drench. (I'm not sure it's wise to inject calcium unless you're sure that's the problem, but you won't do any harm with a twin lamb drench.)
If there's a ketone-y smell about her, then I'd be confident of TLD and give the calcium as well.
I posted my vet's 'Staggers' crib sheet here:
http://www.accidentalsmallholder.net/forum/index.php?topic=12927.msg136877#msg136877If she doesn't seem to be twin lambish, and it isn't just the heat, and she keeps on panting but otherwise not showing any signs of imminently producing, if you get worried you could have a little feel behind - you don't need to use more than your fingers to see if she's opened up; if she hasn't then you won't get your fingers in and she's not ready to lamb.
But in all likelihood, she's just pulling your chain as they love to do and will produce on her own good time!