That’s child abuse. But it’s also an example of how strong beliefs in homeopathy can arise. With fluctuating conditions, people often seek a solution when symptoms (or the child’s cries) are at their worst. When they get better soon after, it creates an illusion of effectiveness.
A similar illusion is at work with the MMR vaccine. Autism becomes diagnosable at around the same age as the first shot is given, creating a powerful impression that the two events are connected.
It’s why we have randomised controlled trials. With no control arm for comparison, your friend has concluded that abusing their child is somehow useful.