If she ate all the afterbirths its pretty normal to have soft stool after that and the stool is often dark.
However bloody stool with mucous is an indication of irritation of the intestinal lining.
This can be due to intestinal parasites, infection such as parvo if she is not fully vaccinated, and irritation if she has been given a lot of treat foods could also cause this.
While dogs can have goats milk for example, cows milk is apt to cause digestive upset.
Low calcium levels can make a dog very ill and you can read about this here
http://www.thepetcenter.com/gen/ec.html
and it has a video of a dog dealing with eclampsia.
If your dog might have gotten into anything toxic, has a rectal temp over 103.5F (normal is 100.5-102.5 Fahrenheit or 38 - 39.2 Celsius ), has gums or tongue that look white, blue, gray or yellow tinted where they are normally pink, has a slow color refill if you press on a pink area of gum or tongue, or is becoming lethargic and non responsive to you then you may want to get the dog in to see an emergency vet if one is available in your area.
This site may help you locate an emergency vet if you need one
http://www.vetlocator.com/hotline.php
You didn't mention what you are feeding her and that could be an issue that I'd be happy to go over with you if you list what she has been eating.
As you need her feeding those pups for the easiest way to raise them you may want to see a vet with her to determine if this is an infection, intestinal parasites (which the pups are apt to have also) or a complication of the whelping.
Hope this helps you!
Any sudden change in food can be an issue in terms of digestive upset.
You might do better with her, as she is so young to be raising a litter, to have her on a higher quality food such as the puppy formula from Chicken Soup for the Dog Lover or Diamond Naturals or consider using regular Canidae which is a complete diet for any age dog. Other good foods include Blue Buffalo, Merrick, Innova, Eagle but if you change foods do it slowly.
I'd plan on getting a fresh stool sample checked for parasites as that is really common in dogs and normally I worm pups at 2, 4 and 6 weeks old and give mom a worming the day after.
To help her out with the digestive upset today, I would suggest a meal or two of a bland food and plain pedialyte added to her water bowl to help with hydration.
I would suggest trying boiled chicken meat or hamburger with the fat drained off, mixed with really well cooked rice in a ratio of 1/3 meat to 2/3 rice to see if that works. Then slowly mix in the food you want her on giving less and less bland food. You may want to give her a dog multivitamin mineral tablet while she is nursing.
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics