In the past, Spinel used to be an innocent gem. A goofy, fun loving personality per say. As she was made to be Pink Diamond's best friend, she became clingy and sometimes unknown to how she felt, always wanting to make her happy.

But when Pink Diamond abandoned her at Pink's Garden, she had changed drastically. 

Due to her abandonment, Spinel is unhinged, prone to spontaneous laughter, and extreme outbursts when reminded even indirectly that Pink Diamond forgot her.