# when the virgins had been gathered together a second time
It is unclear when this second gathering happened, and why. Therefore some versions have altered the text somewhat. It is probably best to translate it as it is written.
Possible meanings are 1) Mordecai sat there so he could hear how Esther was doing from the many people who passed through the gate or 2) "sitting at the king's gate" is an idiom that means Mordecai was given a position of authority by the king.
# the king's gate
"the gate to the king's palace"
# as Mordecai had instructed her
Mordecai told her not to tell anyone about her family.