Hello, I’m so sorry to hear that your twin sister was killed at such a young age and in such an awful way. It sounds as though the prospect of an investigation and the possibility that someone was to blame are adding an extra layer to your grief.
Your loss is so very recent and raw and it is natural that you feel overwhelmed by emotions and frightened of the future. Most people will say that all you can do at this stage is take things day by day or even hour by hour. It’s important to be kind to yourself and allow yourself to grieve - bottling up emotions can make things even worse. Do you feel able to to talk to the rest of your family, or to supportive friends?
Writing things down on this site can also be a good outlet for your emotions. You are among people who understand here. While you wait for more replies to your post, you might also find it helpful to look at other posts in the Losing a Sibling category. There are also these recent posts from others who’ve lost loved ones in road accidents:
@Kirstie posted: My boy
@jannyb posted: Lost my fiancé
There is also an organisation called RoadPeace who have a helpline for families bereaved by road deaths - they can offer emotional support, and also support with going through the investigation process and justice system: https://www.roadpeace.org/support/emotional-support/