Rainbow, I too loved the book 'One Child' and I think I also felt some of what you describe regarding the relationship between Torey and Sheila. I wonder if you have read the sequel to the book, 'Tiger's Child'? It is about when Torey reconnects with Sheila as a teen.
The second book troubled me quite a bit, mostly because I realised how much Torey overstepped the boundaries, and how her 'help' ended up being more damaging to the teenaged Sheila than anything else. It is an interesting read.