Underdeveloped artery in brain(A1) of child with complex heart defects

My daughter has hypoplastic right heart syndrome(single ventricle) and she's had several open heart surgeries. She's now 5yrs old. She has been experiencing bad headaches for a year now and they did a brain/spinal MRI/MRA everything looked good except for a hypoplastic artery in right side of brain(A1). There were no blood clots around it. She continues to have headaches so they are adjusting pain medication to control it. After all of this we saw the cardiologist and he suggested that it may have been caused by the Blalock-Taussig shunt and stenting may be needed.

How common is this hypo artery in association to the BT? Do you know if they usually stent a hypo A1 artery or leave it alone? I read that a hypoplastic A1 increases your risk of stroke. Is there anything they can do to cut those risks? Does low cardiac output cause headaches? We already know she has low cardiac output which causes dilated capillaries in her face(the headaches started about the same time as the bright red face).

Any info would be helpful as we are not scheduled to see the card or neuro for a couple of months. Thanks