Marquistry McGonagall is an OC that i came up with. I also came up with her name. 

Marquistry is pronounced as (mar-kwE-s-tree) and means 'the jewel of nobility'.

she is the youngest daughter of Minerva McGonagall, (secret daughter of Albus Dumbledore), and Morpheus McGonagall. she has four older siblings Merlin, Majesty, Melchizedek and Mystique. there is a 2 year age gap between each of them, however there is a 10 year gap between Mystique and Marquistry. each of them is in a different house at Hogwarts Gryffindor, Ravenclaw, Hufflepuff and Slytherin respectively. However Marquistry is in the rare fifth house at Hogwarts known as Emrys, named after Merlin Ambrosius Emrys. coincidentially her eldest brother was also named after the great merlin too. the symbol for emrys house is the winged unicorn, and its colours are purple and white.
Emrys (2)

Symbol of Emrys House

Marquistry's best friends are Lily Evans and Alice Fawcett. her other friends include the group known as the Marauders: James Potter, Remus Lupin, Frank Longbottom, Severus Snape and Sirius Black. as well as Scorpiana Malfoy and Bianca Zabini.

Marquistry is in a relationship with Sirius Black.