Yesterday was the worse day of my life

So Nala spent the afternoon at the vet's yesterday. They did bloodwork and a urine analysis all of which appear normal. The doc really believes based on Nala's age, 11, and recent history, lethargy and loss of appetite, that it's cancer. Either there's a primary brain tumor or a tumor somewhere else that has metastasized to the brain. I could spend $2000 to find out for sure but really, what good would that do? There's nothing that can be done. It's basically a waiting game. It's times like this I hate being an adult. I want someone to come and tell me exactly what to do so I don't have to make these hard, hard decisions.