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It could be any of those things and more...oral disease, stomatitis...
Ulcers from kidney disease.
The most important thing is that the odor could suggest signifcant tissue death or infection in the mouth and probably due to pain the cat is not drinking or eating. A trip to the vet is needed ASAP...the cat will need IVs if the mouth is too diseased to drink. If there is infection or poisoning, a vet needs to start medications.
Please find a vet ASAP...and let me know if you have further questions.
Thank you for telling me and thanks for taking her in...I am sure she feels better!