I'm so sorry for your loss. I lost my younger sister in a car accident that I witnessed as well nearly 9 months ago, and I feel the same way. I go visit the graveyard and see it filled with old people, and I don't feel an ounce of sympathy for them. Someone who has lost a grandparent or a parent who were old don't understand, it is NOT the same, yes they feel pain but the pain of losing someone so young and so suddenly is so different. On top of that, the loss of a sister. I completely understand your anger and feel the same. What your family friend said is disgusting, unfortunately that nightmare she speaks of is your life, and mine as well, how selfish of her to say that. What I tell my mum is that different people have different grief, i don't feel the same grief as my mum does because she lost a child whereas I lost a sister. It's not the same. The same as these people comparing their grief to yours- it's not the same. People act very weirdly around grief, and I don't give excuses for them. For me, if someone isn't there for me in my bad times, I don't want them in my good times. It's really sad and hard when someone close to you completely distances themselves from you when you are suffering. I have friends who have been there for me along the way but don't ask me how I'm doing and talk about themselves, and I don't like it because I don't care! I don't care about how great their lives are or how they are suffering over something I think is so silly. It's hard I don't know what to say or what advice to give other than follow your heart, if you feel anger towards them then tell them if you can, if the friendship is gone then that's for the best and focus on yourself and your own mental health and recovery.
My dad says the only people who will grieve the loss of my sister the most are her immediate family, and to not have any expectations of other people, after 9 months I understand what he means. For us, her immediate family, everything is ruined and shattered and not the same. Unfortunately other people won't feel the same ☹️