Get it vaccinated, fixed, and a full check up at a vet. Of primary concern is fleas, worms, and ringworm (a fungus, can be passed to humans which requires a cream to get rid of). If you have other cats or plan to eventually, maybe a blood test to check for FIV or feline leukemia. Oh, and register with the city you're in. Not a huge deal but cats have to be registered. If you forget, youll get a mailer.
If the cat is not microchipped and you tried your best to find her owner, and you cared for her more than a month, bring her to the vet, for general health check, and find if the cat is spayed or neutered, if not, find low cost spay-neuter clinic, they often do shots as well. If cat isn't microchipped, do so, if she is, register under your name and address. Do not forget license - depends on the city how much you have to pay. For license the pet should be fixed.
Well go to you local animal shelter find out approiate related shots and obtain lic. Shots are cheaper at spca oakland or milpitas.
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