So my kid has ARFID. I am not a doctor, but what I have learned is that eventually, anything that causes nausea associated with eating can progress into ARFID, even if the original underlying cause resolves. ARFID is technically an eating disorder, like anorexia, but it isn't related to poor body image; it is, basically, a food aversion to, well, food. All food, or nearly all. This is what happened to my kid; there’s an underlying disorder that can be treated with meds, but when not treated causes nearly constant nausea. Once we diagnosed and treated the underlying cause, the nausea didn’t go away. My kid's brain had learned to associate eating with being sick, and that association persisted even when the original illness resolved.

My kid at one point was admitted to the hospital for two weeks because said kid had lost so much weight. They inserted a gastric tube, and kid discovered that kid did not become nauseous when fed through the tube. We knew kid had ARFID, but this was ah “a-ha” moment for kid, because it showed kid irrefutable proof that the problem was not a physical issue with kid's gut. It was very clearly related to the experience of eating. Kid has subsequently learned to “eat through the nausea” as described in the post.

That's what this sounds like. There was likely an underlying physical cause of the nausea; that cause may or may not have resolved, but the nausea is now it's own thing. The OP indicates a series of consults with a behaviorist; I would imagine being screened for eating disorders is what that was about, but ARFID is not a common eating disorder, and may or may not have been considered.