Does energy healing work as a method to fix cardiomyopathy in a child?

Cardiomyopathy. There are multiple kinds of cardiomyopathy. I am not aware of any evidence that any energy type healing has been demonstrated to have any consistent effect on any cardiomyopathy. The standard medical treatments are the best evidenced treatments we presently have. That doesn't mean alternative medicine treatments can't work, it just means that there is no evidence they do.
No evidence. All forms of cardiomyopathy in childhood are serious. The best care for children with cardiomyopathy is delivered in pediatric heart centers with special expertise in caring for children with heart muscle disease. Long-term outcomes are enhanced in cardiomyopathy is delivered according to evidence-based best practices.
Do not know. I do not know of any studies or even anecdotal stories of cardiomyopathy being healed by energy work. That is not to say it will not work. If it feels right and you trust the healer and it is not horrendously expensive then try it. I generally advise not abandoning medical treatment while exploring other options. Trust your instincts.
Alternative. By definition, "alternative" is different than modern western medicine. Generally any drug, herb, treatment, or procedure that stands up to rigorous scientific scrutiny is included in modern medicine. The problem is that many alternative practices, herbs etc do not stand up to scientific scrutiny and cannot be shown to work. cardiomyopathy can be deadly serious in a child DONT risk it.