This is a futuristic dystopian setting. The protagonist is a changeling shifter race that has only a couple siblings and one elder for the race. In the story they are referred to as female. The elder woke up one day long ago and doesn't remember anything before. The one unique thing about these changelings is that they consume energy around them to change shapes.
Time passed and the matriarch elder had kids. The first kid was born or raised incorrectly and went craven with hunger wanting to consume as much energy around. The protagonist finds out about this sibling turning up snuffing out planets and goes to the elder to find out what this is. She is told by the elder the history but does not know how to stop the craven one. The protagonist goes off to find answers and when she is away the craven one finds and consumes the elder with one sibling surviving. They meet up after and try to come up with a plan but the sibling only wants revenge and goes after the craven one and dies.
The protagonist finds a MacGuffin that helps her alter her changing form so she can go to the craven one and starve it out or over fill it. I can't remember that part but the protagonist wins and settles down with a human.