What is the meaning of "wasted"?

As I say, there is no need for Caroline to go out to get information. She sits at home and it comes to her.
My sister continued:
“What did she die of? Heart failure?”
“Didn’t the milkman tell you that?” I inquired sarcastically.
Sarcasm is wasted on Caroline. She takes it seriously and answers accordingly.
“He didn’t know,” she explained.
After all, Caroline was bound to hear sooner or later. She might as well hear from me.
“She died of an overdose of Veronal. She’s been taking it lately for sleeplessness. Must have taken too much.”