She might have something stuck in there, it might be doing damage w/ the blood in the stool. You really should take her in to be seen by the vet in case there is a problem. She may not be able to pass something, and in trying to get her to do so could make things worse.
When they've eaten things like this it's impossible to say. It's best to have the vet maybe do an x-ray.
Welcome to the dog forum...
I totally agree w/ BabaluandOtis,,,you must go to vet or ER for this needs to be examined...blood rectally encouraged into stools show signs of cuts in the intestines,,so please call your vet to be safe...
I would suggest a flushing w/out the safety of vet knowing...
Good luck...
I'm with the other members' opinions on this one. Don't give any kind of a laxative until you know exactly what is in there. If something she ingested is indeed ripping up her intestines, speeding its passage will only cause further damage until it is expelled. If this were only a case of diarrhea for a few days, I wouldn't be too terribly concerned; however, since you notice bloody stools, you may well have an emergency on your hands. Don't waste any more time speculating - just get her to a vet as soon as you can. I hope you'll post back and let us know how she does, and I also hope and pray it turns out to be nothing to worry about. Better safe than sorry. :-)