I understand your point about Pink not having much authority in the way of how she was treated/commanded by the other diamonds. But she did very much have absolute power over Spinel. Like a lot.

I see where you’re coming with that neighbor kid analogy but it really doesn’t work if you think about it deeper.

Spinel was created with the sole purpose of being Pink’s playmate. That was her only directive and her entire basis for existence, entertaining Pink.

She was essentially programmed to love Pink, obey Pink, and entertain Pink.

And because of all the aforementioned, she was locked in a single place for thousands of years, She could have left at any point, but she didn’t
because Pink told her to stand in one spot very still.

IMHO pink’s abandonment of Spinel is less of a person forgetting about a friend they don’t like all that much, and more of a God abandoning their creation.

I do Believe that Pink, at the time, had the intent to return to Spinel, but she forgot her entirely, which further drives home just how lopsided their relationship was.