Find That Book

I read a book a couple of years ago (2016-ish) and cant remember the title for the life of me.

It was about a girl whose younger brother goes missing during her childhood. He was a bright boy and a bit strange, always drawing something (I think it was a map or a maze)
The book follows her through several stages of her life, from the 1970s/80s in her childhood to an imagined near future when she is a grandmother.

I cant remember any characters names or even much of the plot but a few scenes and details stick out.

She runs away from home and gets a job picking fruit at a farm. There's a boy on a bike who she has a romantic link with, they sleep in a barn one night.

There's a moment where she sees a woman fishing on a dock by a canal and she draws something in the dust, it becomes significant much later in the book when some time travel elements come into play.

She witnesses a horrible double murder but gets her memory wiped.

There's a secret society that was involved in the vanishing of her brother. I think her actual brother died very early on and one of its members came to use his body.

she gets married to bike boy and they have children who have children.

In the closing chapters she's raising her grandchildren in a dystopian Ireland where Global resources are running out and society has regressed. the secret society save the children but the whole think is pretty bleak.

I read it in Australia but I think it's set in the UK. I always thought it was Labyrinth by Kate Mosse but having recently got that book and read it i realised its completely different and I'm now very confused.
Please Help.