That's not accurate. She will be able to enjoy all the benefits of *G, even on an Aeroplan award ticket.

Aeroplan, for some reason, cannot add a frequent flyer number to an Aeroplan reward ticket. Even as an AC SE, my Aeroplan # does not show up on Aeroplan reward tickets.

Tell your friend to have her *G card on her, and to present it at check-in. The check-in agent should be able to add it back to the reservation, and her status should show up on the boarding pass. Or if she is checking in online, try adding her UA/A3 # during the online check-in process. She'll need the card anyway for lounge access.