No, it doesn't mean that she was old enough to know better at the time....she was very young or toddler age.
Instead of parroting what you were told it all means by people who politically hate Biden try reading her actual diary.
It's a heartbreaking struggle for her, dealing with her drug addiction....she wants so badly, to be cured...only failing...time and time again.....she uses sex and companionship to try to deal with her addiction...she disappoints herself every time... She admits her lying about her drug use, to her parents and even to herself....
She really loves her mom and dad, and they try to help her get through all of this...
I'm on page 45 out of 120 pages..... I hope and pray she is able to beat her addiction, but where I am at in reading the diary, she's still failing....