You can help her keep an accurate record of her blood pressures to take to her doctor visits along with her medication bottles. Help her eat a healthy diet of fruits, veggies, whole grains, water, low salt. Exercise as tolerated. No smoking, and enjoy a healthy hobby or some sort of recreation. Regular medical check ups to keep blood pressure under control.
This is a tough one to answer as their are many different reasons someone may have high blood pressure. Sometimes if someone is overweight and loses the excess weight they can return to normal pressures. In many people it is a genetic predisposition, so they will continue to have high blood pressure even if they do everything correctly. These are the ones that will need to take blood pressure medication until further notice from their doctor. Most of those with high blood pressure fall into three categories of cause: 1. those with too much fluid in their system 2. those with contraction of the arterioles forcing the pressure to rise 3. those with a high heart rate forces pressure to increase. Someone can also have a combination of these problems as well.
So without additional info I cannot say if diet, lifestyle changes, or medication is what she needs. I can tell you this: you must take care of it as high blood pressure slowly destroys all end organs (brain, liver, kidneys, heart, lungs).
If you can supply more information such at blood pressure numbers, age, body type (heavy-set, medium, or thin) and anything that has been done so far to treat it, I will help where possible