I have linked child tickets on the same airline many times (e.g. me on $, daughter on miles), that is not what this is about.

Specifically, I want to buy a $ ticket for me from AA, traveling IB metal. Then call IB and book the same itinerary for my 8-yo with avios and have them link her so she does not show up as unaccompanied. I understand that "linking" is just an annotation in the record, but has anyone here done something like this? Is there more to marking a minor as accompanied than to just writing a comment in the record?

FYI, this past summer I did something similar with my daughter, separately linking three miles segments on AA and BA for her to my one $ ticket on the same. But the difference was that it was all done by one AA agent.