“this was after Jeconiah the king had departed from Jerusalem.” The Babylonian deportation of Jeconiah and the large numbers of people was in 597 BC.
“queen-mother.” The Hebrew word translated “queen-mother” is gebereth (#01404 גְּבֶרֶת), and in this context the “queen-mother” is the mother of the king (BDB Hebrew and English lexicon). The Queen-mother was the most powerful woman in the kingdom, much more powerful than any of the wives of the king, who often did not have much real power at all.