Because the girl is not the bandit per se, but more of a manipulator. You usually see this in reverse, in fiction and in fact. Watch those late night "women in prison" news documentaries and just about every woman inmate is there because they got involved in some criminal enterprise because of a man or because they struck out violently against a man who had been beating them forever. But I digress.
A man is found in his car by the side of a road with a bad blow to the head. In the hospital, the doctor says that the guy is unconscious not so much because of the wound, but because he's had a shock that his conscious mind does not want to deal with. His wife is by his side at the hospital, not so much because of devotion, but because her husband walked in on her and her boyfriend planning to run away with the fifty thousand dollars that the husband stole from his employer at his wife's urging. The head wound was courtesy of her boyfriend But the boyfriend better beware, because if it was easy for the wife to betray her husband it will be just that much easier for her to betray him.
The "girl bandit" is played by Jeanne Cooper, who played lots of supporting roles in TV over the years and then landed a long running gig on the soap "Young and the Restless". I would say that if the show bothered to label her character with such a salacious title as "Girl Bandit" they should have had her behavior be just a little more cold blooded than shown. We don't even get to see anything that transpires between her and the betrayed husband. I guess such are the constraints of half hour TV shows.