In The Glass Castle, what effects does the unstable, negative environment Jeanette grows up in have on her?
I am writing an essay on how the psychological pain Jeannette went through was caused by her parents.
First of all, from your question, you seem to be presenting two very different ideas. The first idea (in the form of your question) is "What are the effects of the unstable, negative environment on Jeanette?" The second idea suggests you are trying to prove that Jeanette's psychological pain was caused by her parents.
I have a few things you might want to consider. First, I do not suggest setting out to prove that her parents are the cause of her psychological pain. Certainly, her parents and the very un-traditional upbringing she and her siblings experienced is the heart of the book. Rather, what you might want to look at proving is whether she actually experienced psychological pain at all.
When reading your first question (above), my immediate thought is that when you look at the overall tone of the book, the acknowledgements in the beginning of the book, and the author's current sense of self (and success), you might want to write an essay about the irony of the fact that despite the "unstable, negative environment" in which she grew up, Jeanette Walls is surprisingly well adjusted, seemingly happy, and arguably successful as an adult. In that sense, the "effects" of her childhood could be considered more positive than negative. Consider that she developed a sense of self, very early. She is a fighter and a survivor. She has an appreciation for many things taken for granted in this world. She is resilient, and continues to employ the coping skills she learned as a child in her life as an adult.
From the humorous, straight-forward, and often very matter-of-fact tones of the memoir, it is clear the author wishes to portray that her childhood should very well have been considered "abusive," but that it wasn't. Her tone suggests that she never considered herself a victim of abuse, does not resent her parents today, and maintains a very strong bond with a family that should be considered broken and unhealthy. Her story is ironic in many ways and if your essay fails to address the irony, I would warn you that you are missing one of the most prominent messages.