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Unfortunately your information is slightly incorrect. The ACA did allow for bariatric surgery to be a covered service under a standard plan that each state could pick for themselves. Washington apparently does not include that. However, your policy language should be explicit about medically necessary treatment. I had a similar situation with a family member who did not have pregnancy coverage but did receive coverage for her medically necessary c-section, etc.
The only Washington state citation that covers required feeding is http://app.leg.wa.gov/WAC/default.aspx?cite=182-554-300