Donna is Del and the twins' mother who was closer to Del than the boys. From the start of the series, it has been about a year since Donna either left or died and it had a drastic effect on Del because Donna was her cheerleader. She made her feel pretty, smart, valued, and the sudden departure of her person left a gaping hole in Del's life. Hence why, perhaps to feel close to her mom still, she picked up a lot of her mom's bad habits like stealing and lying.
