Who is Lupita from Junky and what is their importance?

Lupita is an established drug lord in Mexico City during the time period discussed in the novel. She is enormously fat, weighing around three hundred pounds, and began using drugs in an unsuccessful bid to control her weight. Only her face got thin. Lupita heavily bribes law enforcement and therefore operates entirely in the open. Her product is very expensive and heavily cut pantopon, but her stranglehold on the drug trade ensures there is no meaningful competition. Lupita is a colorful but minor character in the latter portion of the novel.