These robbers indeed picked the wrong pregnant woman.
Incidentally, you may note one of them was an illegal alien, who'd been charged with burglary previously, got probation and accepted "voluntary return." I.e., he wasn't deported, just signed a paper agreeing to return and was bussed back to the border. That was on Monday: on Thursday he's in Mesa, about 180 miles north of the border, and back into action.
[Update: yes, lucky she moved out of Chicago. If the Mesa PD is anything like the Tucson PD or Pima County Sheriff's Office, they probably told her to ditch the knife and get a gun, offered to put her in touch with their favorite dealer, and gave her a pitch on how easy it is to get a concealed carry permit. I once got stopped for speeding, politely offered the officer the .45 I had in the glove compartment, and he gave me a pitch for getting a CCW permit -- it's so easy and cheap -- so that I could carry it concealed anywhere and wouldn't have to leave it in the car where it might get stolen.]