First -- Nobody and thats including the original poster have stated that THEY have committed the sin --- the poster just asked a general question she would like an answer too. YOU have assumed it to be HER sin.
Secondly - there is benefit in advising in past sins in general IF obviously you no longer commit them and you wish for another to gain benefit from your story/mistakes and for them to avoid them or to show allah's love, mercy etc and how he has blessed you.
And sis -- we must always as muslims live inbetween a feeling of fear for committing sins and our punishment with allah swt but also hope that he will forgive us -- that is why we must stop committing sins once we know better and also to repent and seek allah SWT forgiveness almost constantly throughout our daily lives inshaAllah.
We fear Allah swt punishment but we beg him to forgive us and have mercy on us and only Allah swt knows who he chooses to forgive.