why is tita put in change of feeding roberto? how does she do this?

The ill Rosaura is unable to produce milk and the family must employ Lupita, a wet nurse and relative of Nacha, to nurse Roberto. However, Lupita tragically dies from a stray bullet and the family struggles to replace her. Meanwhile, Roberto becomes increasingly cranky and in an effort to appease him Tita gives him her own breast on which to suckle. She is shocked to discover that she has milk to give the baby.