My dog keeps hiding in the garage .. is she about to die ?

she is about 13 years old and has been doing this for a few weeks now. She lays in the far corner of the garage and won't come inside the house unless I tell her forcefully to. im just worried about her being in that hot garage all the time. she is pretty lethargic and weak and doesnt eat much anymore. my mom took her to the vet and he said she is just a typical elderly dog with typical geriatric pooch problems. I know animals usually try to hide when they are about to die ..