The easiest thing to do is feed your dog a Wellness Treat. Wellness Treats cure all pet illnesses in my experience. You can buy them from the vending machine (Dr. Magi-Heal's Medical Vend-o-matic) at the Brindleton Pawspital.
I don't have For Rent, so I can't test your problem myself, but it seems like the obvious solution would be to transfer some funds to your business.
I'd rather not go all the way to brindleton just to get wellness treats, and you can't transfer funds into a rental house. The revenue is transferred directly to the household funds.
I guess it is what it is.
You could try adding the vending machine to a community lot in your own world. I don't know whether it will work on other community lots, or only on veterinary lots.
You could also try making the Wellness Ttreats yourself on Dr. Magi-Heal's Medicine Craft-o-Matic or on Dr. Budget-Bandage's Medicine Craftidink. The Wellness treat requires level 5 Veterinarian skill.
@OmegaGamer123456 as @Sketch793 mentions the Wellness Treats work and also save time at the vets office itself, you mentioned it takes a long time there so instead of a vet's appointment you can just cut that part out and get the wellness treats from the machine to treat a pet without an examination. It's much quicker and once you've been there and bought a big supply of them you don't have to return. All my pet owner Sims carry a supply of Wellness Treats in their personal inventory.
If you add a vending machine at home it needs to be stocked manually by having your Sim create the treats. Or you can buy some again at the vet's office then take them to your new vending machine to stock it.
If you want a quick way to get some funds I usually get a collecting hobby like fishing, harvesting and collecting. Adding a few plants to harvest can be a real money spinner.
Money isn't an issue in my household, don't get me wrong. I actually prefer to use the exam table for the experience of it. It's just a shame I can't because of this darn bug.
