You got some really great advice here. I had a schnauzer for 17 years and she was blind the last 4 years of her life. She was such a little trooper and never let her blindness hinder her. Her blindness was from cataracts so I never had to deal with the tumor issue. As everyone said, keep things as normal for her as possible and don't move things around. You and only you will know when it is time to let her go. Please make it a decision for her quality of life and not what you think is best for you. Hugs.