There are some things I agree and disagree with. I, too, studied psychology because I loved learning how the mind works and why we do the things we do. That is, until I changed my major <.< Now as a disclaimer, I'm not armchair diagnosing Sarah; I just have a hypothesis that I would like to share to everyone just by observing and researching everything so far. I apologize for this being basically an essay, I wanted to put this in a spoiler but I'm on mobile and can't find an option to do so.
Anyway, yes, I do believe Sarah is insecure. Aren't we all? Yes, Instagram is the most popular platform to showcase a "perfect" life. However, with Sarah, it is much more deeper than that.
First of all, we can't know for sure if Sarah is a homophobe. ( where you at with them receipts @Wedjamin?) But let's just say she is. Let's believe her father's words. He said this all started about when she was 20. The homophobe part, I mean. I'll get to the eye thing later. Any who, what you're saying is that because of the experience with her father cheating with a man, she has become traumatized, triggering her hatred for the LGBT community because she feels betrayed. However, I believe Sarah's homophobia did not originate here, in fact, the whole situation exacerbated it. Sarah has used homophobic slurs, dated before 20. Her favorite being 'fag', her snapchat username being 'fagort', her calling other people 'fag', etc. When she found out about her father's affair, I think she grew more hate for the LGBT community because she wanted someone to blame—that is, her father and the man he cheated with—for ruining a marriage.
Now about the eye thing. It goes more deeper than just being insecure and wanting to be different. Do you remember one of her ex-friends who came forward? She said that Sarah took whatever interests they had and claimed them as her own. There's also that incident where she completely copied tweets and captions from Steak, Blake Anderson's (actor from the tv show Workaholics) wife (real name Rachel Finley). Then there's Sarah stealing pictures from models, wanting people to think it's her. She even goes as far as taking pictures from google saying she visited those places. And, she has plagiarized articles. Do you see the pattern here? No matter what, Sarah copies.
Anyone heard of Borderline Personality Disorder? It's a mental disorder common in most women. According to Wikipedia, "Females are diagnosed about three times as often as males." Signs and symptoms include: disturbed sense of identity, splitting, unstable and chaotic interpersonal relationships, distorted self-image, and the most common—fear of rejection and criticism. American psychologist Marsha Linehan says people with this disorder are "exceptionally enthusiastic, idealistic, joyful, and loving", however, they are also prone to depression, shame, and anger, and other negative emotions. While they may feel euphoria, they are also prone to dysphoria. There are 4 types of dysphoria: extreme emotions, destructiveness or self-destructiveness, feeling fragmented or lacking identity, and feelings of victimization. Reading more on what behaviors BPD experience, one caught my eye—reckless driving. I remembered Mr. McDaniel telling us she crashed his car.
Now let's get to the good part. We've talked about Sarah's compulsive copying. I found many articles and websites about mirroring, one of the behaviors common in people with BPD. On a site called "Out of the Fog", it gives the definition that mirroring is "Imitating or copying another person's characteristics, behaviors or traits." Mirroring is a good tool for people to maintain relationships. My theory is that Sarah wants to be liked and accepted by everyone, that's why she steals all these things from people. It's like finding someone with a common interest; you'll likely end up becoming friends if you both have something in common. This is why Sarah has the need to be sexy, "weird" (as she calls herself), and smart. She wants to be an all-in-one deal. Maybe she saw someone with heterochromia one day and said, "I like that, it looks cool."
Regardless, I think she still needs help either way. She just keeps on lying. My speculation of her having BPD makes the most sense to me, because at least it explains why she is doing these things.
Sources and interesting reads (links are jacked, so you have to hilight and paste them to your URL):