Time period and roles of people in a person's life,  have a relationship so deep, in time. The roles seem to reverse with time and this, can be negative role reversal.
   'Negative role reversal'  as in the cards you play turn up against you not instantly but momentarily. It all roots out from watching and learning with time as the base factor.
   You do good, the universe does good right back. This is what karma is,  but who knew it was so apt.
    Her and I may have been a cooperative team earlier or at least were meant to be,  I mean thats why you have sisters,  don't you?
But the relation between the two siblings significantly depends on the degree of extravagancy exhibited by the older sibling.
    A perfect older sister should be a balance between a monster  and a tooth fairy.  And to strike that balance is no piece of cake. Highly,  utterly  rare.
   The ' tooth fairy'   older siblings do end up having an okay-ish ending. But the ones who suffer are the 'monsters' because  they are  the ones who have  to taste their own monstrous behaviour after the  roles have been  reversed with time.
    So whose  mistake is it? All mine. It is the older that's at fault eh? Yep that's right.
And what  can  be done?  One solution.

'Apologise'.  Start square. Put that ego aside. Reflect upon that incredulous feeling you felt. All that hatred and regret you felt which you wanted immediately to be worn off by time wrapped in the clutches of the wrongs you did.
Start with the word that may seem of mere value because of its incomparable use. But just with the right amount of love and true dedication towards amending errableness, this word is just right to commence.
  A 'sorry'  to begin with.