In general older cats that are thin lack appetite and drink a lot of water are usually sick. Despite the pills to stimulate eating which she does then ok after worn off she is reluctant to eat otherwise ok. If you see any redness inflammation or bleeding of the gums or around teeth there may be periodontal disease present.
Confirm there are no foreign objects or string in the mouth or under the tongue. If your cat has lost its appetite known as Anorexia this can be a clinical sign of many diverse health problems for example dental disease mouth injury or anxiety and stress it may or may not mean your cat is experiencing any sickness. But usually a decrease in appetite will be one of the first signs of a digestive system problem. If the flavors are too intense or it lacks taste then he may be disinterested or.