I don't see any other responses yet. Others may have more information than I do.
I work with computers and the internet a lot and there IS a lot of misinformation out there. "Google it" is starting to be used quite a lot! I could "google" this subject but my advice would be along the line of getting more than just one doctor's opinion. I know there are some pediatrics departments who share perplexing problems or consult with one another when there are questions, but I've only found one such place years back.
Please get another doctor to examine and evaluate your child. The worst case scenario would be that your child would be no worse off. You might even learn more ways to help you learn ways to work with and help your child.
I really dislike "I told you so attitude" especially from a doctor. She told you about her evaluation and you weren't convinced the helmet thing was worth its price. She could have been nicer or at least not mention regrets like that. If there was anything to regret it should be that she hadn't suggested getting a second opinion (or third even).
You have a lot of mothers thinking of your story and praying all turns out well.