I am very sorry to hear about your girl Coco's loose stools with blood. I understand she has had issues long term with intermittent diarrhea.
Of course anyone would be concerned about blood in the stool. The fresher the blood appears the closer the source is to her rectum.
The important factor in all of this is how your she feels. If she feels great otherwise, is willing to eat and is active then that is a good sign.
Is she vomiting or does she seem nauseous (lip licking, repeated swallowing and stretching)?
There is a condition in dogs called hemorrhagic gastroenteritis. These dogs have profuse dark, jelly-clot like, bloody diarrhea. They are very sick dogs and get dehydrated quickly so they need immediate care. Thus if she seems very lethargic and/or begins vomiting an emergency veterinary visit is best.
But colitis or inflammation of the large intestine can cause bleeding and increased mucous production, as well as the urge to pass stools even when very little is present, which leads to straining. Colitis can be due to stress, a change in diet (even just the addition of new treats or a different flavor of her usual food), parasites, a viral or bacterial infection, inflammatory bowel disease or even a food allergy. Rarely a mass in the colon can be the cause, or exposure to anticoagulant rodenticides. Another possibility is an anal gland infection. These are scent glands that are located just inside the rectum and an infection can cause a bloody discharge, though should not cause loose stools.
A raw, irritated colon can take a few days to heal. The bleeding should clear completely with treatment over the next 2 to 3 days. If not she should be checked by her regular veterinarian and her anal glands should be checked. Well worth checking at least a couple fresh stool samples too as parasite eggs/cysts are shed intermittently and they may be picked up on the second sample or third test even if the first is negative.
If she still feels fairly well now though we can try some things at home, but if you are feeling uneasy about how lethargic she is an emergency visit is never a bad idea.
If her appetite is off and her stomach is gurgling she may have some stomach upset and reflux that can go along with bloody stools.
To try and settle her stomach today you can give either:
1) Pepcid-ac (famotidine) at a dose of one half of a 10mg tablet per 10 to 20 pounds of body weight every 12 hours.
2) Prilosec (omeprazole) at a dose of one quarter of a 20mg tablet per 10 to 20 pounds of body weight every 24 hours.
These will reduce stomach acid and should help if this is related to simple nausea and gastrointestinal irritation. Either one can be given for several days if need be. If her appetite is great and there are no signs of nausea you can skip this step.
I would not feed her any food for 12 hours. This should help stop gut spasms and restore normal gut motility. Small amounts of water or ice cubes given frequently are fine as she needs fluids after all that she has lost with bloody stools. You can give her pedialyte to replace electrolytes too but Gatorade is much too high in sugar which can make colon irritation worse.
Today even with the fast you can start Kao-pectate at 1/2ml per pound or 1/2 tablespoon per 15 pounds of body weight every 8-12 hours. This will coat her irritated gi tract as well as absorbing bacterial toxins. You can use it for several days until her stools look normal. You can find kao-pectate at the drug store.
If she has a tense painful abdomen, continues to have diarrhea with no improvement after being on kao pectate for 24 hours, becomes very lethargic, begins vomiting or runs a fever greater than 103.5F then she really must be seen by a veterinarian as soon as possible. Make sure to take a fresh stool sample with you when you go.
After her food fast start a bland diet of 1/3 boiled, lean hamburger (or boiled, white skinless chicken), all fats and juices drained off the meat, mixed with 2/3 boiled, plain white rice. Feed several small meals a day. You might wish to add 1 tablespoon of canned pumpkin (not pie filling, just plain pumpkin) to each meal as fiber helps soothe an irritated colon. I recommend adding probiotics like Fortiflora, Proviable or Benebac to her meals daily to re-establish normal gut bacteria levels too.
Once she feels better (no bloody, loose stools for 48 hours) start mixing in her regular dog food very slowly. Less bland more regular with each day. It should take a week or so to convert her back.
If your pup begins vomiting and feeling poorly though it would be best that she see a veterinarian now as anything you give her orally will just come back up worsening her dehydration.
To address her long term intermittent diarrhea it is important to describe what sort of loose stools she has to try and localize the problem. Loose, small stools with mucous or bright red blood and straining or urgency to pass stools more frequently point more towards large bowel diarrhea or colitis, whereas watery stools with no mucous, no increased urgency or frequency to go, along with weight loss point more toward small bowel disease.
It is quite possible that she has a food allergy/sensitivity or inflammatory bowel disease and that she needs a different low residue, easy to digest food or a hypoallergenic food to be able to properly digest and absorb her food and not have loose stools. I highly recommend a trial of either Hills i/d or Purina Pro Plan Veterinary Diets EN if she has mostly signs of small intestinal disease. No treats, table food or edible chewies while she is on her food trial. If she does well she can eat these foods for life as they are balanced. Dogs with food allergies can benefit from Hills z/d or Purina Pro Plan Veterinary Diets HA.
Dogs with signs more related to colitis can be fed Hills r/d or w/d or Purina Pro Plan Veterinary Diets DCO (colitis diet).
Dogs with inflammatory bowel disease and colitis will worsen with stressful situations. There may be times when she will need medications too, such as metronidazole or even steroids if that is her problem, but I have found that a consistent diet formulated for their disease process is very helpful for long term control.
There are other possibilities too for intermittent loose stools.
Addison's disease, which is a poorly functioning adrenal gland, can lead to chronic diarrhea and vomiting. These dogs cannot handle stress at all because their adrenal gland doesn't produce cortisone when stressed and their electrolytes can be off too if their adrenal gland isn't controlling that normally either. We see vomiting, diarrhea and sometimes physical collapse in severely affected dogs. Testing is an ACTH response test to check adrenal gland function and checking electrolyte levels. Treatment is steroid replacement therapy and electrolyte replacement.
Pancreatic insufficiency is another possibility. These dogs have a pancreas that produces a decreased amount of digestive enzymes, and the amount produced can wax and wane in some cases, especially early in the disease process. Testing is by running a blood test called a TLI which checks for digestive enzymes. Treatment is replacement of digestive enzymes at each meal. An easier to digest food would be expected to create less problems with digestion and as such less diarrhea.
In short diagnostics need to be done if diet alone isn't helping. They can be as simple as more fecal checks and cultures, as well as checking pancreatic and/or adrenal gland function. An abdominal ultrasound could be very helpful. Or more invasive testing such as biopsies of her gastrointestinal tract to look for inflammatory bowel disease or infiltrative cancers such as lymphoma an be done.
Best of luck with your pup, please let me know if you have any further questions.