I can sympathise with her, when moving from France to Spain, my mom carried all of her jewellery in her carry on. The Transavia gate agent had her check in her bag at the gate saying the couldnt accomodate any more carry ons on the plane even though she told them she had valuables in it. Well you guessed it, when in Madrid, the bag appeared torn apart on the conveyer belt with every bit of valuable item gone. Everything. She cried for days and Transavia offered something like 100$ compensation. Off course she sued but by the look of it it's not going anywhere.
I think the best tactic for pax being asked to check valuables is to whip out the 'old smartphone and video record the agent making the request, open the luggage and video record the valuables, and then video record the luggage being taken away. Make sure you get the agents nametag in the photo.
On two occasions, I have had rank-and-file check in agents make serious errors on check-in (once in DEL, the other in ABQ). On both occasions, I recorded the incident to howls of protest from the check-in agent. On both occasions, a supervisor appeared who couldn't have been more helpful.