Is a 70 year old woman with mild copd and asthsma likely to need oxygen full time in the near future?

Depends: May not be if you take care of yourself. If smoking quit. I assume the disease is mild, hence I do not foresee use of oxygen unless a sudden deteriation. Advised flu and pneumonia shots.

Probably not: Probably not if her COPD and asthma are really mild and she does not have any other conditions that may affect her breathing (heart, lung, neuromuscular etc). A pulmonologist who examines her and does pulmonary function tests and/or an oxygen requirement assessment will be able to give you a more precise answer.

Not Necessarily : Asthma is reversible . COPD is not reversible. Most pts requiring oxygen is because they have chronic hypoxemia. It is common for COPD to turn into chronic hypoxemia requiring constant oxygen but much less for asthmatic pts unless they are in constant "status asmarhicus" or develope cor pulmonale with cardiac insufficiency.