No, I don't think it would have an adverse affect on children suffering from life-limiting illnesses, or pain, or chronic illness, or physical difference.
Because, in the end, we only do have this one body. It's as stark as that. Whatever this body is, that's it. It's a fantasy, a mirage, that one can have the 'wrong' body. And I think it's actively harmful for children to internalise that idea.
When children are in crisis, we might be more attentive to the books or media we present them with - what is right for one child right now is not right for another child right now.
Maybe a child needs texts that affirm their anger right now, or acknowledges their despair. This is why children have parents and librarians and health educators and even bibliotherapists to help them in their book choices.
Maybe another child, dealing with the exact same thing, finds the message of the book healing.
There is nothing inherent in the book which is damaging to unwell or disabled children, imo.