Dara... you are not guilty of anything.
What happened to your sister and parents was the consequences of their actions, nothing more nothing less, you... are victim.
And even centuries that you "lived" cursing people, it still isn't your responsibility, I won't say all those people deserved it or it wasn't a bad thing, it would be irresponsible, but... you still aren't responsible for that.
You were quite literally cursed, deprived of your life and peace in death, forced to be fused to a being made of hate and rot.
But just the fact that your mind still was able to come back after those centuries, and who you are now is the same gentle and caring person you were in life and that you still feel guilty about what your body did, is undeniable proof of your character.
But please... don't deprive yourself of this little happiness that has finally come to you.