Hi,
at this age they do dehydrate and will get weak fast if they do not eat.
1- does she eat her food since she has been with you?
2- was she weaned and on cat food before you got her?
3-Are the other kitties of the litter healthy?
4-She might be the runt of the litter because she does have health issues
5- She may have contracted a virus like panleucopenia
6- She may have a large load of intestinal worms, or have other parasites, caution some are transmissible to humans.
7- Did you give her cow milk?
Because of her serious symptoms, i am sorry to say but I would see your primary care veterinarian as soon as you can. If they are closed tonight, you should go to the ER.
Try to see if she would swallow a little bit of water with an eye dropper, keep her warm in the meanwhile. Do not force her to drink, you may cause some aspiration in her lungs.
Let me know if you need additional information.
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Veterinarian
20 yrs of cat dog practice, general practice, emergency, certified in veterinary acupuncture 2006