The third paragraph tells us that Kahlo typically used traditional symbols calling back to the Aztecs to represent a strong and indigenous Mexico. The author then gives us an example of this in one paining, in which she represented herself between an industrial US and a preindustrial Mexico surrounded by the symbols in question. This is a specific example of an earlier generalization.
While the paragraph does include a contrast, that is in the painting, not the structure of the paragraph. The paragraph is not contrasting different things, it describes a paining that happens to.
