What details in the story suggest that Mrs. Jones was a large woman?

In addition to the several times that the narrator actually uses the word "large" to describe Mrs. Jones, there are a few other details that help us to get a sense of her size. For example, Mrs. Jones has a very large and very heavy purse. It is, in fact, so heavy that when the boy tries to steal it from her, he actually falls down as a result of its weight. Mrs. Jones must be a fairly sizable person, as she seems to carry it with ease. In addition, she is able to keep a hold on the boy, lifting and restraining him even when he starts to struggle; her ability to do this also indicates her size. Later, once they reach her house, the boy thinks make a run for it, but when he looks at her, he thinks twice. He must be somewhat intimidated by her, and this likely has something to do with her size as well.

There are certainly details in the story that suggest that Mrs. Jones was a large woman.
The first paragraph uses the word "large" to describe Mrs. Jones. The first sentence of the story tells us that Mrs. Jones is a "large woman with a large purse that had everything in it but hammer and nails." 
When a young boy tries to steal Mrs. Jones' purse, the text tells us that "the large woman simply turned around and kicked him right square in his blue-jeaned sitter."
During their conversation, Mrs. Jones remarks upon the boy's dirty face and asks whether there is anyone at home to tell him to wash his face. The boy answers “No’m,” which prompts Mrs. Jones to declare that she will wash it for him that evening. The text then tells us that the "large woman [started] up the street, dragging the frightened boy behind her."
At the end of the story, the text tells how the boy looks back "at the large woman in the door" as he leaves her house.