[1] She was born Margaret Hilary Ashworth in Halifax, Yorkshire, the daughter of the local assistant head postmaster, and was educated there.
She continued her studies at St Mary's College, Durham[2] and went on to Oxford University, where she earned a PhD in 1968 with A. O. L. Atkin as her advisor.
During her husband's two-year posting in Germany, she taught mathematics at an Army Education Centre there.
[2] Although her career was cut short, in 1983, the London Mathematical Society organized a symposium on modular forms.
[1] In a tribute to Millington, Atkin said "I have no doubt that, had she lived, she would have made exciting original contributions to a field which has at last come into its own again, after nearly a quarter century in the doldrums, and where there are now at least twenty first rate people of her generation working actively.