Why does Dade let the woman go at the end of the story "Star Food"?
It's quite possible that Dade lets the woman go because he feels sorry for her. Also, if we follow the text, it's quite clear that Dade has never been comfortable with the way his father expects him to deal with shoplifters.
As a young boy, Dade is torn between the differing expectations of his parents. While his mother believes that Dade will achieve some vague quality of "limited fame," his father prefers him to think about more practical matters. Since Dade will inherit the store, his father expects him to learn the intricacies of running a grocery successfully.
However, Dade spends most of his time contemplating the sky after he cleans the dead insects off the star-shaped incandescent light fixture on the store roof. Meanwhile, his father becomes extremely frustrated with him and worries that Dade will ruin his future. On the other hand, Dade's mother thinks that he just needs more time to navigate his "worldly curiosity" towards the realm of some grand discovery. For his part, Dade doesn't know what he wants.
The title of the story illustrates the conflicting forces bearing upon Dade: while his mother wants him to reach for the "star" of some vague, future scientific discovery, his father wants him to concentrate on food, specifically the business of selling food to customers.
While he tries to figure out his life, Dade notices that a woman has been stealing from the store. He lets her steal twice before he confronts her. When he finally apprehends her, the experience isn't as satisfying as he imagines it will be. He sits her down to interrogate her in the way his father has taught him to question shoplifters. However, the older woman is no child, and Dade feels strange using the same methods he would use for younger shoplifters.
The woman is thin and clearly undernourished; in the end, Dade decides to let her go. He leads her out the way his mother has always led out the younger shoplifters. Dade walks part of the way home with her. He realizes that when his parents sleep that night, his mother will "dream of discovery" and his father will "dream of low-grade crooks."
When he thinks about this and the old woman, he feels sad. Neither of his parents have taught him how to know himself or how to relate to others. They have presented him no other options in life than the ones they have put in front of him. So, Dade lets the shoplifter go because he feels sorry for her and also because he still feels ambivalent about who he is and what he really wants out of life.
Dade lets the woman go because he gets to know her and understand her, and he decides he likes her.
As Dade sits on the roof dreaming, he thinks about how he can change his life and become the son his parents want. He daydreams about the sky, with its “waves and shifting colors, wind seams and denials of distance.” The sky makes him feel small.
It was blue liquid. I spent hours looking into its pale wash, looking for things, though I didn’t know what.
It is on this rooftop that Dade decides to make a change. He plans to be more active at catching shoplifters when she sees the military jets fly overhead. Unfortunately, when he catches the woman she just stares at him. He does not have the heart to turn her in, so he lets her go. First he lets the woman go because she steals pineapple juice, and he pities her for stealing something so insignificant. The second time he lets her go and actually walks part of the way home with her. He realizes that he is not cut out for this life.