And I'd like to repute that argument, but I think that she probably could empty a whole clip into an intruder. She's a pretty cool customer.
Take her to the range and have her do several pushups or jumping jacks then shoot at the target at the longest distance that she might have to use her firearm.
Then tell her to make her eyeball shot. Assuming that doesn't convince her. Let her shoot again, but right as she is getting ready to shoot. Scream really loud or use an air horn, something to startle her. But be ready to keep the gun pointed down range if she jumps and tries to turn.
Lastly. Ask her, if the .22 LR is as useful as she is thinking it is, why it isn't used by police/military all over the world as a defensive weapon. Because nothing is a cheap or easy to shoot as a .22 LR so why not use it.