Her mum died, dad met someone else. KK was treated like the outcast she is and did not feel loved. Her sisters probably got all the attention. So KK would act out just to get their attention because any attention is good attention right (something she still practice's today). Her sister grew up, they were the 'pretty one' and the 'clever one'. KK continued to feel unloved as she went in to her adult years, they had had enough of her attention seeking s. So they would keep her at arms length - in true KK style she 'blocked' them from her life before they could reject her.
Please feel free to correct me KK if any of this isn't ringing true.