The Book Thief. Why did Liesel’s mother abandon her? At what point doesn’t Liesel understand why her mother had to abandon her?

From the text:

I think her mother knew this quite well. She wasn’t delivering her children to the higher echelons of Munich, but a foster home had apparently been found, and if nothing else, the new family could at least feed the girl and the boy a little better, and educate them properly.

Her mother was constantly sick and there was never any money to fix her. Liesel knew that. But that didn’t mean she had to accept it. No matter how many times she was told that she was loved, there was no recognition that the proof was in the abandonment. Nothing changed the fact that she was a lost, skinny child in another foreign place, with more foreign people. Alone.