If you want to make a case Vriska is a self insert, I think it would make sense looking at Z from Psycholonials. She is very clearly a Vriska, and her situation in the story mirrors Hussie own experience handling the Homestuck fandom.

Even then, it seems very unlikely to me Vriska was created with such intention, so she is not a "self insert" by definition. Maybe since Hussie has identified more with her, but that is a different thing. And Vriska herself hasn't been written by Hussie since *at least* the Epilogues, if not since the end of Homestuck proper.