I'm sorry to hear your cat is not feeling well. Being a 'senior', it would really be best if she were evaluated by the vet, as a cause of loose stools in cats may indicate intestinal parasites, inflammatory bowel disease, intestinal viral or bacterial infections, and food allergies.
While I agree with you re: not changing foods at this time, if her current food contains corn, gluten, artificial additives and preservatives, these, and other ingredients, are common allergens for cats, and I'd recommend a premium cat food like Wellness, Newman's Own, Felidae, or Natural Balance, available in major pet supply stores. You can offer a little at a time, mixed with the present food, until she's gradually changed over, but you can wait until after this stomach problem has passed.
Since her last blood work was 2 years ago, it's time for another test, to make sure all her levels are within normal limits. Older cats can develop diabetes, hyperthyroidism and kidney issues more often than younger cats, so a blood test every year or even every 6 months, would be best.
For now, you can try to feed her only bland food for the next couple of days, to try to get her stools back to normal; plain jarred baby food chicken (no onion/garlic added-check the label), and/or plain boiled skinless chicken breast mixed with plain white rice, should help. Also, add 1/2 teaspoon of plain, unflavored yogurt to a small portion of one of these foods, daily, and it will help increase the 'good' bacteria in her digestive system, plus, it should help firm up her stools.
Also, add 1 oz. of unflavored children's Pedialyte to her water bowl, if you're sure she's not diabetic. Her electrolytes need to be replenished, as she could be dehydrated, due to the loose stools over so many days.
If you're in a financial bind right now, the following organizations may help you find a lower-cost vet and/or one who will treat her free of charge:
is a credit card for veterinary visits and medications and might be of use for you at this time, as it enables you to pay out the vet's fee in installments, but the vet gets paid up front by the company.
I hope your furry girl is feeling better, very soon!