children's book - necklace, Victoria Albert Museum, ghost, pink wall

[catspear]

hello! I am so desperate to find this book. I read it as a kid in primary school. I rented it from a library and even a few years after I couldn't find it again and it's been driving me mad since (I am now 30!) so it was late 90s im guessing, and seemed an oldish book. The only thing I can remember was something about a ghost, and a necklace that ended up being exhibited at the Victoria and Albert museum - maybe the necklace was haunted? I know there was a ghost in it and maybe a brother and sister, but am sure the lead person was a young girl. Also there's something about pink and a wall - I'm not sure if book cover, title or what but I'm desperate to find out' if anyone has an idea please let me know!