Please note the following is in no way legal advice. It part personal opinion, part administrative analysis. The Schools subforum has plenty of existing resources to advocate for your child's educational and disability rights for whosoever should want them. I would point towards Wrightslaw as the best single starting point.
Students with disability who qualify for protections under IDEA, 504, and ADA do not lose those rights simply because a doctor tweets his personal belief. Rather, to do so may constitute discrimination by stating a class of protected persons based solely on their disability should be treated DIFFERENTLY than any other student with disability eligible for the same protections. Replace anaphylaxis with HIV or diabetes and it will become more obvious how contrary to nondiscrimination such gross statements are.
Whether that individual should hypothetically be held accountable through a wide variety of accountability mechanisms will be up to: if those accountability mechanisms are brought into play; by whom; and if implemented in an effective manner (i.e., not malicious). Accountability mechanisms could be employer policies or administration, state law, city ordinance, federal law, agency regulation, ethics committee, hospital or city ADA coordinator, professional nongovernmental oversight (such as bar association or state licensure), or private right of action under 504 or ADA for damages.
There may have to be a course correction implemented by large hospitals to hold their physicians accountable for statements that may cause harms, especially when they violate institution nondiscrimination policies, or constitute unauthorized practice of law. I can't imagine many medical schools attached to state or publicly funded institutions having risk management departments that would not be sensitive to such events once they are made aware of them.
One should be aware of the caveats in seeking accountability of persons in high profile professions. Expect an institution to circle wagons over liability concerns for its employee and potential law suits (even where there is no litigious intent whatsoever), retaliation and character assassination of the person filing the complaint ("you are a dumb Facebook mom/anxious/hysterical/helicopter parent", ad infinitum), rationalization or justification for the person's actions or statements ("I'm only trying to help, why do you hate kids/facts/reason."), and to get blocked by administration.
A reasonable expectation in this hypothesis is some internal institutional corrective action in exchange for your individual humiliation getting dragged by their social network including sycophants, perhaps with a hint or so of sexism by resolution phase. No one will ever admit any wrongdoing even when it does truly amount to simple error in judgment.
