Music was your connection and your play.
Those pieces must have been the most beautiful sounds you ever heard.
To have that stop suddenly would be a huge loss. And would be something a 9 year old could not comprehend - you must have wondered how could Mom not possibly bring the piano that brought both of you so much joy?! You must have wondered if she missed playing as much as you missed hearing her play, and if she missed the connection too.

Like a metaphor for play and joy in one's life.
It sounds like things were pretty serious and not so joyful after that move where the piano was left behind.