First blog post :D! Many people have covered this topic before, but I am putting my own spin on this. So many people treat rose's actions like an adult (which she is), but think about this, pink was treated like a child so much by the diamonds (for example, her getting "grounded".) I'm not saying she didn't act like one, with her temper tantrums and such. She had the mind of a child, and she should kind of be thought of as such. I think she thought she would come back for spinel, because she was going to be gone for a single DAY as rose. She would have come back, but she got so stuck with earth that she forgot spinel (and spinel would probably have been shattered in the war). Even though I'm saying she isn't TERRIBLE, she still did some bad stuff. The war shattered thousands of gems (probably close to millions), and she left everyone behind when Steven was born. I think she didn't know what she was getting into, but she should have learned about all of this beforehand.
I haven't watched the entire show, but I know the entire plot, so correct me if I made any mistakes!