A book involving a child with missing mother, transported to magical world/forest & comes across a harpy

Question

I read this book in 2009/10 in grade 8/9 for English and would love to find the name.

The details I remember include a boy or girl (pretty sure it's a young girl) with missing/presumed dead mother and they find or were given either a box/necklace that belonged to the mother. I believe the father is still alive in this. The child opens it/puts it on and is transported to a magical world. I think when the child is transporting, the father rushes at them, trying to stop them but it's too late.

After the transportation, I vaguely remember the child finding themselves in a strange forest in which I recall the trees and surrounding environment visually looking like Polyhedrons but this may just be how I interpreted it. The child comes across a harpy that (from memory) seemed to know of the child's mother. The harpy woman comes across as stern and difficult to talk to at first but was willing to help the child in their quest to find/find out more about the mother. The gist of the story is that the child goes through this world searching for answers about the mother and who she was and finding out about who they are also.

Answer 1

Thanks to everyone who viewed this and commented.

After sorting through some house stuff, I actually found my English review of this book I was describing. It's different from how I remember it but it's definitely the one! :) The book is called It's Time, Cassandra Klein by Karen Brooks.

When Cassandra receives an exceedingly ugly necklace for her birthday from her long-lost mother she is reluctant to try it on, but when she does she finds herself in a startling new world. Morphea is her mother's world - a place where the myths and legends of our world are a lived and continuous reality. When she is pursued by a witch called Hecate and kidnapped by the Ferryman Charon, she must find her way back home and rescue her father from the sinister Dr Proteus. But will she leave this place where the pull of her mother is so very strong?