Thanks for answering my questions.
First of all, you get a gold star for being so observant of your dog! So many owners (myself included), let the dog out into the yard and I couldn't honestly tell you the last time my dog defecated because I assume he does it out in the yard. So kudos to you for being a much better pet owner than most.
Dogs may have a little bleeding or discharge from the rectum for a couple reasons: damage done to the rectum while defecating, certain types of cancer, impacted/infected anal glands, parasite infection and polyps are just a few.
If there is only a small amount of drainage around the area, I would just keep an eye on it for now. Sometimes dogs will try to pass a large amount of fecal material and can cause small tears in their rectum. These generally will heal on their own without any sort of medical intervention. Feeding the dog some canned pumpkin (make sure that it's only real canned pumpkin, not the pie filling) can help make the stool a little easier to pass, thereby helping to not tear things any further.
Parasites such as worms and protozoan infections such as coccidia and giardia can produce blood in the stool and blood from the rectum after bowel movements. You can read about these here:
A problem with the anal glands can also cause a bit of bleeding. You can find more information on those here: http://www.dr-dan.com/analsac.htm .
You can read about rectal polyps here:
Whatever the cause, rectal discharge is never normal and I think it's a VERY good idea that your dog is going to be seen by her vet tomorrow. I strongly suspect that it's just a small tear from the history of less frequent bowel movements over the weekend (meaning she may have been a little constipated) and then having diarrhea that followed it, but it's good to have her looked at just to be on the safe side.
I hope this helps.
I hope this helps!