Donna Diamond is the current wife of Steve Douthwaite, a very elusive witness in the Bamborough investigation.¹

Not only is Donna shocked to find two private detectives at her B&B in Skegness, but she’s also so surprised and upset by her husband’s history and potential involvement in the case that Robin fears she might pass out.² (Because her upset is so great that it hampers their interview with Douthwaite, Strike wishes she had.)³

Donna has a Scottish accent, short dyed yellow hair and a “deep vertical line … graven down the middle of her forehead.” ⁴  

^{1: Troubled Blood, Chapter 63
2: Troubled Blood, Chapter 64
3: Troubled Blood, Chapter 65
4: Troubled Blood, Chapter 64}