From the symptoms you describe, I would be highly suspicious of a tooth ache or dental disease. Cats will often paw at their mouth, rub their face on the ground, drool, have bad breath, eat less or choose to eat wet food rather than dry food.
Sometimes dental disease can be hard to spot in a conscious cat, especially as some disease can be below tooth level and requires x-rays to diagnose. With very thick calculus, red gums
or loose teeth
the dental issue is easier to spot in an awake cat.
If one vet thought a tooth needed removing he would have said that for a reason, so likely spotted something, hence I would be more inclined to side with him. Perhaps the other vet missed it.
Other possibilities exist including oral ulcers or mouth cancer. A very thorough mouth exam is advised and sometimes a mild sedative is needed to achieve this in a feisty cat.
Given her age and concurrent medical condition, she may not be the best general anaesthetic candidate and so it would not be a straight forward decision as a dental cannot be performed without an anaesthetic.
If it was felt that her quality of life was poor due to her dental issues and a dental is her only option to live a comfortable life, a dental (+/- extractions) could be performed though would be high risk. A pre anaesthetic blood test to assess an up to date liver/kidney function as well as intra-op fluids would be advised . Her thyroid would also need to be stable.
If an anaesthetic is not something you would consider, she may benefit from some medication e.g. pain relief, anti-inflammatories and antibiotics to control any oral infection and pain. These should be started asap.
I would ensure she has plenty of soft, warm tasty food and that she is encouraged to maintain her hydration with warm chicken broths and water. Consider a high calorie food such as Hills A/D as well as warm chicken and fish little and often.
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