
Coprophagia, eating poo is fairly common, and there are a number of reasons for it.
Having the runs means anything your dog has eaten wont have been fully digested, so she may be trying to 'recycle' the nutrients from it.
Other reasons are as suggested, she may be trying to hide the evidence, or it could be boredom, or a dietary deficiency.
Get the pup checked over by the vet, make sure it doesnt get the opportunity to do it, ie pick up poo straight away, and make sure the pup is well exercised trained and played with, so she isnt bored.
Good luck with it, its a pain having a dog that does it, i have got one who will sometimes eat his own, yeeeeuch.
Eating other animals poo, ie horse poo, cat poo, sheep poo is fairly normal, not to be worried about, but eating its own poo, or other dogs poo is something to get sorted out.
Em