Tumor? What to do?

[Rashy]

I`m checking as I dont know what to do. As I told before, Tassen is not well. The vet found a grey spot in one of her lungs, she have been at antibiotics but Tassen does still have issues. Some told me that a grey area at a xray does usually means that it is a tumor.
I dont know what to do as the vet told me that if the sound dont gi away, it might be better to put her down, and some means that I should get a second opinion. As for now she does come out of her house and getting food, drinks water, and sleeps. She does not run in her wheel. Her weight last time at the vet were 35 g.
In total she did go at the antibiotics 17 days, the antibiotics she did get is the on the vet thought were best.

Should I just let her be, and see how the days go?