In Like Water for Chocolate, how come Tita is breastfeeding her nephew when she didn't get pregnant until near the ending of the book?

In her novel, Laura Esquivel uses a fictional style called "magic realism", a technique found frequently in Latin American Literature.  In magic realism, elements of the fantastic are intermingled freely with the realistic.  Tita, caring for her baby nephew when his wet-nurse is mortally wounded, is at her wits' end when the frantic baby refuses to take cow's milk or tea.  Out of desperation she offers the child her own breast, thinking it would "at least act as a pacifier and keep him occupied while she decided what to do to appease his hunger".  She is shocked when she finds she is able to actually feed the baby - it is nothing short of "a supernatural act" (Chapter 4).  The magic of this particular situation is one of many which Esquivel uses to reflect of one of the main themes of the book - the intense emotion created by the love between Tita and Pedro which cannot be thwarted.