First Lady...No First Daughter

Why are some media organizations referring to President Donald Trump's daughter, Ivanka Trump, as the "first daughter"? As I don't recall those organizations using that terminology when referring to the daughters of former Presidents Obama, Bush and Clinton, why now? What's next? A "first son"? Reducing the significance of the role enjoyed by the "first lady", or the soon-to-be more accurate "first-spouse" or perhaps in the not too distant future "first-partner", with these other overstated "first's" it can diminish the importance of the informal title.