I read this children's book about 5 years ago, it was a small, charming little book. It probably was published in the past 10 years. It was in Afrikaans, but I'm fairly certain it was a translation from English (or potentially Dutch).
I got it from a library in South Africa (I've asked the library about it and dug through the kid's section again several times but can't find it!).
Since I read the Afrikaans translation I'm not 100% clear what the English translation was like, but here are the key points:
A little girl lives on her own, her parents are collectors (I think?) and are away a lot. She has all kinds of collections of things. She's a human girl and most of the people in the books are people (unless otherwise mentioned).
Her guardian is called Mr Knuffels (in the Afrikaans translation. This isn't really a proper Afrikaans word, but a dutch one). It means "cuddles" in English. Mr Knuffels is a weird furball creature from the swamps of Norway.
There is a monster in her basement that she's friends (?) with and she sees when she does laundry down there.
She has a pet (a dog?) and there have been dog-nappings in town and she tracks down a dog-napper and solves the mystery.
The book is small (A5 size, if not smaller), pretty thick and has charming drawings of the layout of her home with her collections, newspaper clippings, and other cute diagrams.
Given the use of the dutch word "Knuffel" and the reference to Norway, it's possible this book had origins in europe, and potentially was originally written in Dutch. Knuffel isn't really used in South Africa very commonly.
I would love to find this book again and read it to my daughter, if anyone has any ideas.