Good morning @amandarosendahl and welcome to Mayo Connect. I am so sorry that you had a difficult relationship with your sister. When did you make the decision not to let your sister define you? In saying that your don't want your sister to define do you mean you don't want to be like her? My twin sister was an addict at 15 years of age. She was very ill equipped to handle this type of life or any situation that didn't offer her the type of acceptance and love that she ached for. We were very loved but our mother didn't know how to raise twins (does anyone?) and set up a very competitive environment for us. We were fraternal but a lot of people confused us. I was afraid that in certain situations I'd look like her or act like her.I in no way wanted to be anything like her.
We all have moments of "Oh woe is me" and that's fine. I mean people can be every mean and hand us a pile of crap. But we can survive and look at us now!! PTSD is a symptom of that, accumulated over a period of years. PTSD doesn't just mean that only one things causes it.
Can you tell me more about your situation? Have you been in more control over your PTSD in recent years?