I spoke with her vet. She was just in about a month ago, diagnosed with Pancreatitis.
Anyway-they asked if she's eaten anything new. Yes...she occasionally gets into Bella (our puppy's) food. She's also been eating grass and such outside (a sign to me, she's not feeling well). She's fully vaccinated, and during her visit a month ago had a stool culture run (it was negative). So, they are glad she's had one recently. They said to keep an eye on her, and her stools today...and call back if she continues to have bloody stools.