Ahasverosh is searching for a new queen. He has his guys round up all the pretty women in the neighborhood and prepare them for a beauty contest of sorts. The winner would be anointed queen and all the runners-up would be relegated to the second women's house as part of the general harem.
We find Esther being taken and preparing herself to meet Ahashverosh. It finally is her turn to appear before the king. In 2:15 it tells us, "ובהגיע תור אסתר בת אביחיל דוד מרדכי..." - when it came the turn for Esther the daughter of Avichayil, uncle of Mordechai...
Why describe for us now all of her lineage? Previously when it first introduced Esther it did not tell us she was the daughter of Avichayil. Why now, after we already are familiar with Esther, does it feel necessary to introduce us to her lineage, when before it did not?