Share 'My English Setter has lung cancer'

My Daisy started coughing 4 days ago and after taking her to the vets who did a chest x-ray has told me that she has lung cancer and actually wanted to put her to sleep straight away. However she was running round the garden last week and I don't feel that she should go just yet.  Does anyone know of anything that will extend her life without making her suffer?  She has got pain killers and the v…