There isn't any particular reason to celebrate daughter's day. We mark this designated day to remind the society that our daughters are our joy, and there should not be any patriarchal beliefs attached to their birth.
While different countries celebrate it on different days, it is usually observed on the fourth Sunday of the month of September, every year. In India today i.e., September 22 is being celebrated as daughter's day.
Children are a blessing, whether male, female, or other. They should be cherished daily however it's nice to take a day out to honour them in particular.
Take a look on to few daughter's day quotes