Respected user, Hi I evaluated your query thoroughly.
*Leucocyte esterase positive reaction means +Ve microscopy as >50 
leucocytes per mul &/or organisms seen.
*Reasons include any bacterial infection by gram +ve / -ve organisms
  affecting urinary PH by ways of 
dehydration , 
skin infection , fungi invasion,
  breach in hygiene of private parts & many more.
*Precautions to be taken :
 - give plenty of liquids preferably boiled water, coconut water, rice water, 
   boiled milk , home made juices , butter milk.
 - avoid oily / spicy / nonveg stuffs / beverages.
 - keep her private parts clean & dry .
 - loose , cotton , clean underwears.
 - avoid tight clothings / sanitary pads .
 - continue medicines as per your doctor`s advise .
 - watch for her skin turgor , playfulness, 
fever , screaming while micturition
   immediately 
consult Pediatrician in such cases where you suspect problem
 Hope this clears your query.
 Thanks for using Health care magic & keeping trust in our medical services
 Wishing her fast speedy recovery from the same.
  Regards dear take care.