In the Holy Scripture, nothing is said about the fact that after ascension to heaven, Mary was crowned. Nevertheless, from the 12th century a tradition appeared and became very popular to embody this theme in religious art.
In the picture, the crown is not yet put on the head of the Virgin Mary. Coronates her Holy Trinity. Mary is between the Father and the Son, who crown her with a crown, and above them a dove, the Holy Spirit.
Related Paintings 
Immaculate Conception by Diego Velasquez 
The Coronation of Mary by Francesco di Giorgio Martini 
Coronation of the Virgin Mary by Fra Beato Angelico 
Portrait of a Lady with a Fan by Diego Velázquez 
Christ in the house of Martha and Mary by Diego Velasquez 
Aesop by Diego Velasquez 
Infanta Maria Anna, Queen of Hungary by Diego Velasquez 
Portrait of the Infanta Margarita by Diego Velasquez
Immaculate Conception by Diego Velasquez The Coronation of Mary by Francesco di Giorgio Martini Coronation of the Virgin Mary by Fra Beato Angelico Portrait of a Lady with a Fan by Diego Velázquez Christ in the house of Martha and Mary by Diego Velasquez Aesop by Diego Velasquez Infanta Maria Anna, Queen of Hungary by Diego Velasquez Portrait of the Infanta Margarita by Diego Velasquez