Brief Answer:
Cardiac and inner ear evaluation should be done!

Detailed Answer:
Hi,
Firstly thanks for choosing health care magic for your query!

Hypertension,old age,Supraventricular tachycardia points toward some structural or physiological problem with heart.
It can be symptoms of underlying coronary artery disease--If there is a blockage in coronary arteries supplying the heart the pumping functions are affected , hence heart will maintain blood supply when body needs are minimal(when she sits she feel better),But while walking or doing regular work as the demand increases ,it can't be met hence person can feel light headed and dizzy. SVT and arrythmias can also be because of ischemia to myocardial muscles.

i would suggest you to go for -
2d ECHO- to rule out motion abnormalities in wall of heart and to know if ejection fraction is normal.
Tread mill test-An exercise stress test is primarily used to help to determine if your heart receives enough oxygen and proper blood flow when it needs it most, such as when you are exercising.
2d echo and Tmt taken together have a sensitivity of more then 85% to rule out CAD.
A carotid doppler -A carotid Doppler is an imaging test that uses ultrasound to examine the carotid arteries located in the neck. This test can show narrowing or possible blockages due to plaque buildup in the arteries due to coronary artery disease.Carotid artery supplies blood to brain ,blockage in it can cause symptoms like dizziness,fatigue,presyncope.

Though her blood pressure is varying a little ,yet dizziness and light headedness would not be there at sytolic 110 or 141.

HUTT test-head up tilt test-A tilt table test,is a medical procedure often used to diagnose dysautonomia or syncope. Patients with symptoms of dizziness or lightheadedness, with or without a loss of consciousness (fainting), suspected to be associated with a drop in blood pressure or positional tachycardia are good candidates for this test.

A thorough evaluation of cardiac system is required to find the cause of svt,dizziness and fluctuating blood pressure.

However diziness and light headedness can be also because of involvement of inner ear (labyrinth) ,hence a pure tone audiometry and caloric tests could be done to rule out involvement of inner ear.Weakness and extreme fatigue are often associated with dizziness due to inner ear.
In case you need more explaination,feel free to ask!

Advice
Follow up with report.

Thanks,
Dr Rishu Saxena
Cardiologist

---