Albert Barnes Commentary 1 Chronicles 4:18

"And his wife the Jewess bare Jered the father of Gedor, and Heber the father of Soco, and Jekuthiel the father of Zanoah. And these are the sons of Bithiah the daughter of Pharaoh, whom Mered took." — 1 Chronicles 4:18 (ASV)

His wife—that is, Mered’s. It seems Mered had two wives: Bithiah, an Egyptian woman, and a Jewish wife whose name is not given (as noted in the margin).

If Mered was a chief of high rank, Bithiah may have been married to him with her father’s consent, since Egyptian kings often gave their daughters in marriage to foreigners. Alternatively, she may have chosen to leave her own people and commit to a Jewish husband, converting to his religion. Her name, Bithiah, meaning “daughter of Yahweh,” is fitting for a convert.