Do you know if you mother has any problems with high blood pressure? High blood pressure can cause headaches. Also, has she seen a neurologist in regards to her headaches? It may not hurt to see a specialist to see what is causing these headaches. Your physican or the specialist would be better able to answer your questions as to why your mother has these headaches.
Here is some information that James Castle,M.D. said in regards to headaches after strokes:
"Headaches after a stroke are fairly uncommon, but they might occur for the following reasons:
1. a redirection of blood flow when healthy arteries stretch and grow to supply blood to the part of the brain that has lost its normal supply
2. stretching of the brain's covering from scarring, swelling, or atrophy of the brain
3. small amounts of bleeding into the area of the old stroke (less likely)
4. a small tear in an artery (also unlikely)
If you're concerned, talk to your mother's doctor. The more dangerous of these possibilities can be excluded by imaging the brain and its blood vessels. Imaging should also rule out the possibility of recurrent strokes or TIAs. If the images don't show any major problems, it means the headaches aren't likely due to anything serious."
Hope this will help you get some answers,
Here are some links that might be helpful:
Sunshine to Lower Blood Pressure
Have High Blood Pressure? Don’t Eat These Foods
10 Things to Do This Month to Lower Your Blood Pressure