Oh man I am happy it was not parvo but really concerned for her health now. Get some pedialite or something similar and a feeding tube if needed and get something substantial in her. I would seek out another vet and get a second opinion. What did the vet do regarding the worms? 7 weeks to me is to young to be away from the mom and you mentioned you got her at 6 weeks. The shelter did not check for and deworm her? If the vet did not give a worming shot or liquid you might want to buy some SafeGuard from Amazon (get the stuff for goats they give directions for dogs by the pound) check with a vet to see if the dog is strong enough to be given a 3 day dose of Panacure/Fenbendazole (SafeGuard).
Dosage info.
Safeguard Goat Dewormer Suspension 10% (100 mg/mL) has Fenbendazole as its active ingredient and can also be used to worm dogs. It is useful against the most common canine intestinal worms including whipworms, hookworms, roundworms and tapeworms. It is even effective at fighting giardia. I use it regularly when worming my own four dogs and I know many multiple dog households, rescues and shelters that use it as well because it is much more economical than Fenbendazole wormers marketed for dogs such as Panacur C.
DOSAGE AND DIRECTIONS FOR DOGS:
Shake bottle well and then measuring with an oral medication syringe give 1 mL (equal to 1 cc or ¼ teaspoon) per each 5 lbs. of your dog's weight mixed with a small amount of moist dog food (to make sure the dog consumes it all). Repeat this dose for three days in a row. For giardia, repeat dose for 5-10 days in a row.
Newly weaned pups (6 to 8 weeks of age) should be dewormed at 6, 8, 10, and 12 weeks of age. Treat the dam at the same time as the puppies. Dogs over six months of age should be dewormed, if not monthly, at least twice each year. Each deworming requires 3 daily treatments.
NOTE: The dosage above is for 20 mg of Fenbendazole per pound of your dog's weight.
The dosage for goats is only 2.3 mg per pound as opposed to 20 mg per pound for dogs. This is because goats and dogs are different species, have different physiologies, digestive tracts and metabolisms and also because different worms are being targeted in each (you can call Safeguard customer service and they will confirm this as will any veterinarian).
IN GOATS fenbendazole targets: Stomach Worms (Haemonchus contortus, Teladorsagia circumcincta).
IN DOGS fenbendazole targets: Roundworms (Toxocara canis, Toxascaris leonina), Hookworms (Ancylostoma caninum, Uncinaria stenocephala), Whipworms (Trichuris vulpis), and Tapeworms (Taenia pisiformis) as well as being effective against giardia.
Because the dosage for using fendendazole in dogs is 20 mg per pound and this suspension is 100 mg of fendendazole per 1 mL (equal to 1 cc), that means 1 mL (or 1 cc) will treat 5 lbs. of dog (confirmed by my dog's veterinarian).
Panacur C dog wormer uses 888 mg of fenbendazole per 3 day treatment for a 40 lb. dog which is equal to 22.2 mg per pound so their dosage is just slightly higher than 20 mg per pound of dog.
The Pill Book Guide to Medication for Your Dog and Cat actually recommends a dosage of 23 mg of fenbendazole per pound of dog given for 3 consecutive days.
SAFETY:
Fenbendazole is very safe. Doses up to 100 times the recommended dose of 20 mg per pound are tolerated without serious side effects. It is also safe for use with pregnant and lactating dogs as well.
An accidental overdose may cause minor vomiting and diarrhea. It is also possible that dogs might experience hypersensitivity reactions to dying parasites. If facial swelling, hives, scratching, vomiting, shock, seizures, pale gums, cold limbs or lethargy ensue, your dog may be experiencing an allergic reaction. In cases of accidental overdose or allergic reactions you should contact a veterinarian immediately.