Fatigue and weakness may be associated with mild anemia, or dehydration. Drink more water, fruits and vegetables containing more water content like ash guard, cucumber, watermelon, etc. Take iron rich diet like spinach, dates, curry leaves, amla, etc. Menopause may also cause these weaknesses.
Next Steps
If she's not on any antihypertensive or Diabetic medication, can give her ORS solution if it's only necessary depending on her condition.