Optic nerve decompression surgery makes a hole in the dura mater lining around the optic nerve to shunt cerebro-spinal fluid into the orbit behind the eye. It's a low pressure system and shouldn't create a should loud enough to be heard.
When one hears noises in the head or ear the concern is there is a leak (fistuala) from a high pressure system (like the arterial blood vessels) into a low pressure system (like the veins or cavernous sinus of the head).
I would suggest you discuss this again with Dr. Trobe, the neuro-ophthalmologist. He may want her to have a MRI/MRA or to see a neurologist.
JCH III MD Eye Physician & Surgeon