So can Vriska only control people below her on the hemospectrum? Is it everyone, like could she control Terezi? I thought for some reason Aranea can control anyone, regardless of blood color. If so, does that mean Vriska could eventually control any troll or is that just cause Aranea is really strong?

It has nothing to do with the Hemospectrum order, given she can’t control Aradia. It’s all about mental fortitude. With enough time, she may be able to control everyone just like Aranea.