ABANDONED. Book about kidnapped child with a sister nicknamed Sparrow (post contains spoilers!)

[Just]

I read a book in maybe 2015/16? (may have been 17) that started with a small child being kidnapped in a park. The child had a much elder sister named Chloe who was nicknamed Sparrow.
The book was set in the UK.

(view spoiler)[

Sparrow was in University I think, and her ex-boyfriend was the son of the kidnapper. I believe he had committed suicide and it drove the kidnapper crazy. (hide spoiler)]

[Rainbowheart]

Still looking, Just?

[Becca]

This sounds like While My Eyes Were Closed by Linda Green:

‘You OK, Sparrow?’ Mum asks as Chloe comes into the room. I haven’t heard her called that for years. When she was younger she used to get called nothing else.

[Kris]

No response, moving to Abandoned folder.

Just (OP) last posted in the group in July 2018.