Hello, looping back around to let everyone know how it turned out. Despite having been told to visit an AF ticket desk to sort out the situation, my wife called Flying Blue customer service the following day and simply asked to book a flight for her second friend (the one that had been denied booking online the prior day), as if she'd never tried to do so previously. She mentioned nothing about being flagged previously (if that's what indeed happened). She told the CSR that she'd tried to book online unsuccessfully and she'd prefer to try over the phone. CSR left the phone four or five times over the course of a 30 min call. Much to DW's delight, the seat was booked and confirmed with no problems.
Humorously, AF media team DM'd her later in the day after she'd booked seat (she had posted something earlier in the day). They told basically "sorry, we can't help, go to airport ticket desk." She didn't bother arguing.
Anyway, this data point seems to indicate that being flagged for fraud on a new FB account after a transfer of partner miles (in this case, URs) and attempted award booking doesn't necessarily require a ticket desk visit. If at first you don't succeed online, try you luck over the phone. Thanks for all the good input and guidance everyone!