A revolver probably makes the most sense overall, but I think a DAO would be best considering they won't practice or likely even hardly handle the weapon and sound like people who would most likely completely panic in an actual defense scenario. No need to weapon that can be cocked to single action. Maybe even something with a bobbed hammer so they can precisely see how it works. Ruger makes a bobbed hammer SP101 that might fit the bill. If they insist on keeping it unloaded, I would probably say get a semi-auto and maybe they will keep it C3.

Regular practice is ideal, but even without any training, ordinary folks can effectively defend themselves with firearms. We see numerous news reports of such cases where even small children have done so successfully. Guns truly are the great equalizer. The idea that they are better off without one because they don't train is nonsense as far as I'm concerned.