Good Morning Clare and welcome to Just answer. I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
As long as Chewey is still eating well, I would not be too concerned about this diarrhea with blood. I say this because a mild digestive disturbance caused by stress or something she may have ingested will cause irritation to the very senstive rectal mucosa which causes small blood vessels to break and bleed. This will resolve once teh stool is back to normal.
For now, Clare, as long as Chewy is still eating, treatment is as follows:
Fast Chewy for 24 hrs which she may be doing herself to allow his tract to calm down and heal..
Give Chewy Pepcid AC at 0.5 mg per pound every 8 hrs.
Give only small amounts of water or ice cubes.
After the fast, feed a small meal of rice and boiled chicken.
If she is feeling better, then wean her back to her regular meal. If she is still haveing btrouble , especially because of her advanced age, I would have your vet or the ER vet examine Chewy just to be sure we have not missed something important.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please Reply so I can clarify for you
Sincerely, XXXXX XXXXX