15 Then Esther sent this reply to Mordecai: 16 "Go, gather together all the Jews who are in Susa, and fast for me. Do not eat or drink for three days, night or day. I and my maids will fast as you do. When this is done, I will go to the king, even though it is against the law. And if I perish, I perish."
King Xerxes had already deposed Queen Vashti for something much more trivial, not showing her beauty. By the way another act of civil disobedience.
Yes, I am not arguing that the king had given as a law that you could not come to him without being summoned. However, the king also provided a means whereby someone could come to the king and not die. Civil Disobedience seems to me to imply a kind of continuing resistance. Ester did not make any kind or continuing resistance because there was none for her to make. She was welcome into the presence of the king.