Isobel Ross was born to Mr and Mrs Ross, granddaughter of the gifted witch Minerva Ross, in a small village in Scotland. At age eleven, she received her acceptance letter and headed to Hogwarts School of Witchcraft and Wizardry, where she was sorted into Gryffindor House.
Isobel graduated at the top of her Charms class at Hogwarts, and having been Captain of the school Quidditch team. She, like her grandmother and her parents, had proven herself to be a most gifted witch, both in sports and in classes.
Sometime throughout her teenage years, she had slowly fallen in love with the quiet and serious young Muggle Robert McGonagall, a neighbour in their village. Knowing her parents would disapprove of her dating a non-magical person, she kept their growing relationship a secret until their abrupt eloping when she was eighteen years old.
Robert and Isobel eloped, marrying and having a blissful honeymoon to the anger of both sets of parents. She could not bear to mar the bliss of the moment by revealing to him that she was a witch, and as such kept it quiet. The two moved into a manse on the outskirts of Caithness, where Isobel proved most adept at making the best of Robert's pitiful salary.
On 4 October, 1935, the couple's first child, Minerva Mary McGonagall, was born. Her birth proved both a joy and a crisis, and soon Isobel was locking herself into her room with the baby for hours on end, trying to conceal the spontaneous magic that erupted from the infant.