If your vet is old school, he may not be aware that three years ago, Pepto Bismol changed their formula. The new stuff is very toxic to the cats. I would encourage you to cease feeding her anymore of the pink stuff.
If her stool looks black and she is pooping on the floor- it is a sign she is quite ill. You can find out if she is pooping blood (which is what it might be) by taking a jar you don't much care about and filling it with warm to hot water. Drop the stool into the jar and see if the water turns red. If it does, she needs a vet PRONTO.
I would also strongly urge you to get her spayed. She becomes open to some nasty infections being unspayed- and some of what she might be in line for will kill her fairly quickly. I am sure there is a low-cost spay and neuter clinic in your area- they are pretty much all over the United States these days.
Please see if you can find another vet one that keeps up with the times.
ASPIRIN (ACETYLSALICYLIC ACID, SALICYLATE) Pepto-BismolSources Many analgesic, antiinflammatory, antipyretic, and anticliartheal (Pepto-Bismol) agents that contain salicylates are sold as OTC preparations. Some keratolytic products contain salicylates.
Mechanism of action Acetylsalicylic acid inhibits cyclooxygenase, which then inhibits production of certain prostaglandins, including protective prostaglandins of the E series. High levels are known to directly stimulate the respiratory center (early) to cause an initial respiratory alkalosis. High doses are also known to uncouple' oxidative phosphorylation and may cause hyperglycemia and glycosuria.
Clinical signs The biologic half-life of aspirin is 7.5 to 8 hours in dogs and 38 to 45 hours in cats at a dose of 25 mg/kg/day. The toxic dose in cats is >25 mg/kg/day in cats and >50 mg/kg/day in dogs. Signs are noted within 4 to 6 hours after ingestion of a toxic dose and include depression, vorniting, anorexia and lethargy, tachypnea (caused by initial respiratory alkalosis), and hyperthermia. The vomitus may be blood-tinged from GI ulceration. CNS depression leads to muscle weakness and ataxia; coma and death can occur within I or more days. Gastrointestinal ulceration or perforation may be seen after the administration of repeated doses over several days' duration. Anemia, bone marrow depression, Heinz body formation (cats), and toxic hepatitis may occur.
Toxic signs may be seen at doses of Pepto-Bismol >7 mL/kg/day in dogs and cats. Two tablespoons of PeptoBismol contain the salicylate equivalent of one 5-grain aspirin tablet.
Treatment There is no specific antidote. The stomach should be emptied by induction of emesis or lavage if within <2 hours of ingestion though there are literature reports that gastric evacuation may be of value up to 12 hours after ingestion of enteric-coated aspirin preparations. Multiple-dose activated charcoal is warranted. Acid-base balance is corrected as needed; diuresis is instituted. Alkalinization of the urine with sodium bicarbonate can be done to hasten urinary excretion, though this requires intense monitoring and is difficult to achieve safely. Peritoneal dialysis allows direct removal of salicylic acid from serum. Gastric ulceration or perforation is treated as needed.