I am sorry to hear about your wife. As you know stage 3b lung cancer is an advanced stage, not 100% curable, but yes, treatable to some extent. Taxotere is a good drug but its efficacy depends on how advanced is the cancer (size or primary and secondary infiltrations), her liver function, her general condition and her power to tolerate the drug. Usually this is given intravenously every three weeks and the action is immediate with some improvement coming with every cycle. At times radiotherapy is given in combination for better symptom relief. It is very difficult to access how soon the drug will bring appreciable difference. I am sorry, but this is something you need to discuss with her treating doctor. Also, please find out if it will help to register for a clinical trial with newer drugs. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.