Negative thinking style. You don't know what she is thinking, nor do you know her exact intent, unless she says it.
Put aside the trauma, are you dependent upon her? Why do you think her sister is saying such things to her about you?
Its easy to blame someone else, but it is you who is here saying its time to end your life all because of your friend breaking away from you. Honestly, if you were sucking the life from her, knowingly or not, due to your own depression and trust issues, then that would be why her sister is telling her to stay away from you, because you are not in a healthy place.
If you surround yourself with healthy people, good people, often your life is good. If you surround yourself with people who such everything good about you, from you, then your life turns to shit.
This is not a blame game, its an honesty game because it is you who is ill from trauma. We have to look inwards at ourselves, heal ourselves, before we can often have any other relationships. Its not uncommon that two people with traumatic lives can be friends. Where those relationships often break, is when one heals faster than the other, and that person realises how much the other is sucking from them, when trying themselves to keep their head above water and continue to get better mentally. Before they know it, they end that friendship, or they push the other person away at arms length, changing the friendship dynamic.
It's like this - if you're a drug addict, then chances are you're hanging around other drug addicts. Quickly enough, non-addicts will push you out of their lives because you want to be destructive and your behaviour is being destructive in their lives, so they make a choice at some point. Suddenly your in a relationship with someone, a drug addict, but you want to get clean, yet your partner doesn't. One of two things happen, you break apart or you turn back to drugs, contrary to wanting to get clean.
Life is about choices, and we often have to look at ourselves before we just blame others, especially when we are the ones with mental health issues. When we become healthy, you can look back and see how destructive your life has been, but until in that space, that view isn't an optionwas hoping to find support on this page, people understand what I'm going through, instead