We first meet young Zahara in Career of Evil when Robin goes to warn her mother about Noel Brockbank.¹ Robin’s choice to ignore Strike’s warning to stay away from Brockbank and attempt to save Zahara is the thing that causes him to (briefly) fire her.² 

Shanker assisted Robin with her rescue mission and became acquainted with Zahara’s mother, Alyssa.³ 

In Troubled Blood, it appears that Shanker is living with Alyssa when he mentions Zahara twice to Strike.⁴

^{1: Career of Evil, Chapter 54
2: Career of Evil, Chapter 55
3: Career of Evil, Chapter 54
4: Troubled Blood, Chapters 26 & 27}