Who is the narrator, can she or he read minds, and, more importantly, can we trust her or him?
3rd Person (limited and omniscient); 1st person (central and peripheral)
Since García reveals information through many lenses (i.e. Celia reveals things about herself, but other characters supplement that with their own stories about her), the narrative technique is quite flexible. Felicia's sections are always told in third person, but the narrative voice can be either limited or omniscient. In "Baskets of Water," we feel pretty firmly entrenched in Felicia's fevered brain—until we get a glimpse of Otto's lust. Celia's narrative moments are in the third person, and are generally limited to her own observations and thoughts.
Celia does pen her letters in first person and although they are poetic and fluid, they focus firmly on her experience and feelings (central narrator). Pilar's and Ivanito's first person narratives also stick close to their own perceptions of people and situations (also central). Herminia and Luz speak in first person of their own experiences, but their accounts exist to tell the stories of other characters (Felicia and Hugo), which gives them a peripheral voice.