I hope your mother recovers quickly. Based on original studies, someone with a grade 4 COPD (which is also called "very severe" COPD) has a 60% chance of living 3
years. If we are talking about a grade 3 COPD (also called "severe" COPD), then there may be an 85% chance of living 3 years. Everyone is of course going to be different. Your mother's younger age (less than 65 years) gives her a bit of an advantage, but the continued smoking probably more than cancels this out.
More recent studies have shown that beyond the grade of the disease there is a better predictor of the prognosis of COPD, called the "BODE" index. This predictor includes other factors such as the results of a breathing test, combined with the extent of shortness of breath, the distance one can walk in 6 minutes, and the body mass index. The BODE index can easily be done in a physician's office.
There are several things your mother can do to improve her prognosis, the most important one being complete smoking cessation. Other possibilities include using oxygen (if her oxygen is low), and perhaps the use of inhalers treatments (which can also reduce her risk of flare ups such as the one she now has). It is always a good idea to stay active, and I would suggest participation in a pulmonary rehabilitation program. In addition to the exercise part, such a program will often include discussions and help on smoking cessation.