How different is the final draft from the draft sent? If it is materially different/better, I don’t think you have any choice but to make the correction as each school instructs. No doubt many, many applicants have hit the “send” button prematurely, so I suspect there will be some level of sympathy from the AO’s as they understand the stress that these kids are under. Support your kid and try to make light of this. No sense adding stress and anxiety to the situation.
Just as a tip for future applications/online submissions. Draft them in Word and paste in the final draft when completed. Do not keep prior drafts. Edit over the existing draft. If for some reason you feel it is necessary to keep an interim draft to be re-purposed later, save that in a separate folder with a completely different name.