So I fully understand, the gun is loaded, and when she pulls the trigger, nothing happens? Or when she pulls the trigger, you hear a snap and the gun does not fire?
One thing to look at, is the opening lever being closed all the way? Sometimes with ammo, dirt, lack of shutting smartly, even lint or clothing getting in the way, the lever does not fully close and will then evidence itself in not having the lower barrel fire.
Second idea, get a new cocking plate for the lower barrel. Or have the current one welded up.
https://www.midwestgunworks.com/winchester-101/parts.htmlMike