I am Dr. Snow, and I can try and help you with Moose. In an older cat with normal bloodwork and fecal tests, a possible problem would be intestinal disease, such as inflammatory bowel disease. IBD in cats can cause weight loss, vomiting, anorexia, or diarrhea, in any combination.
Sometimes, adding in a probiotic can help. There are some available for cats that you can obtain over the counter (such as Amazon) or there is one called Fortiflora your vet should be able to prescribe.
This condition often responds to a diet change, such as a limited ingredient diet. Natural Balance is a brand that makes some good limited ingredient diets, such as venison and pea. A limited ingredient diet can help decrease inflammation in the intestines.
In addition to probiotics and dietary changes, intestinal disease in cats often is very responsive to oral steroids, so you may want to inquire to your veterinarian about this.
Providing multiple litter boxes and scooping them often may also help. It may be uncomfortable for her when she defecates, and sometimes they associate that with the box, so giving her options may help.
Please post back with further questions,