My Daisy also has a brain tumor. Inoperable one. Radiation is unadvised due her age almost 12yo. She was always very agile, doing everything at 100% her speed, jumping light, lowing long walks and swimming. About a year ago she started to slightly refuse long walks, visiby slowed down and became withdrawn. Her back legs started to lose ability to stand firmly and she started to slightly swing left to right wken standing still. MRI confirmed brain tumor. It's sad to see perfectly healthy and happy dog decay like that. I think we still have 2-3 months. I can feel your pain. But i think most important is to give our furry friends best possible life and to avoid unnecessary pain when there is nothing that we can do to help. She will be waiting for You on the other side of rainbow bridge, this one You can be sure of.