I thought the air bladder in the well pump pressure tank would dampen this spike in water pressure. Apparently not.
Daughter mentioned the problem started after the toilet tank parts were replaced. This caused the tank to fill much faster than it did with the old parts. I suggested she turn the water supply valve to slow down the fill time. This solved her pipe hammering problem.
I noticed this faster tank filling when I replaced tank parts in one of my bathrooms a year ago. I have had no hammering problem.
New parts tank fill time 30 seconds, old parts tank fill time 55 seconds.