Should I put my dog down or not?

My 10 year old half Chihuahua half Fox Terrier dog was diagnosed with a brain tumor 5 months ago in September. We've put her on medication which has semi-helped stop the seizures, but now she has gone blind in both eyes. Many people are telling me to just put her down. I just want what's best for my dog and want to stop her pain and suffering. I know she is going to die sooner or later since there really is no cure other that surgery for a brain tumor. I know putting her down is the most humane thing to do since she is suffering, but at the same time I feel like I'm just giving up on her (and she has NEVER given up on me!!)!! :'( I don't know what to do, should I wait it out and see if she can adjust to her recent blindness and live a relatively happy life (even if it is short), or should I just put her down?