I think the rationale for having Suzie Homemaker pull her LCP out of her purse is that she'll act as a speed bump. The more time the (fill-in-the-blank's) spend dealing with her, the less time they're able to spend targeting the other innocents in the vicinity, and if she gets some hits and kills one that's a bonus. We're not expecting her to turn into a SEAL Team Delta Recon Ranger after an 8hr concealed carry course and a box of ammo at the range (though we'd obviously love for her to seek out quality instruction and increase her capabilities). Her role if she chooses to intervene is to at least slow the process of targeted killing down while waiting on a police response.
Your contributions have been interesting in this thread. Thank you for them.