"Nijn" is the second syllable of "Konijn" (Rabbit) with "tje" being the diminutive.
So her name is an affectionate kid version of "Little Rabbit".
I have know idea where "Miffy" came from.
(and for dutchies, it's a long way until 11 november, but here's an early reminder for the times of covid: https://www.youtube.com/watch?v=ZRkqkBjlmqw )
"Nijn" is the second syllable of "Konijn" (Rabbit) with "tje" being the diminutive.
So her name is an affectionate kid version of "Little Rabbit".
I have know idea where "Miffy" came from.