John Gill Commentary 1 Kings 9:24

"But Pharaoh`s daughter came up out of the city of David unto her house which [Solomon] had built for her: then did he build Millo." — 1 Kings 9:24 (ASV)

But Pharaoh's daughter came up out of the city of David
Where he placed her when he first married her, until he had finished his buildings, (1 Kings 3:1), which being done he brought her from thence unto her house, which Solomon had built for her; the reason of which is given, not only because it was the house of David, but because it was holy by the ark being there for some time; and therefore he did not judge it proper that his wife, an Egyptian woman, and sometimes in her impurity, should dwell there; see (2 Chronicles 8:11),

then did he build Millo :
this being particularly repeated from (1 Kings 9:15), and following upon what is said of Pharaoh's daughter, has led many Jewish writers to conclude her house was built at Millo; and indeed, without supposing this, it is hard to conceive why it should be observed here; the Targum on (2 Chronicles 8:11) calls her name Bithiah.