
You're best to call the vet or pop her in for a check with the nurse.
Sometimes bitches have bleeding from the "stump" - ages ago when I had a GSD spayed all of a sudden she poured flesh blood from her vaginal opening. I called the vet, he explained what it was - and that was the end of it, she was fine.
Meanwhile, I would be very careful with her because she can open internal stitches - she's not healed. If she is pulling hard it is as bad, if not worse, than running.