Did you ever end up switching her staple diet to something healthier than pellets? She might be developing a calcium deficiency or another nutritional deficiency. She needs a vet ASAP.
Try to warm her up, burrito wrap her in some fleece and push fluids or juicy fruit on her, try to get some sugar into her, it may perk her up while you're on your way to the vet. Your vet can give her more fluids if she's dehydrated and advise on how to treat her. You'll have to act fast if she's fading this quick. Hope she pulls through, keep us updated!