Based on what disqualifier?
She was born in Manhattan, which was part of the USA last time I looked. And, her birth certificate is not forged.
And she is old enough.
So why isn't she eligible?
Her mother was not a citizen of these United States at the time of her birth.
We have heard, ad nauseaum, on this forum that "Natural Born Citizen" means born on US soil to parents who were both citizens at the time of birth. Ivana Trump was not a citizen of these United States at the time that any of her children with Donald Trump were born.