In Genesis 26:34 Basemath is the daughter of Elon the Hittite, and one of the three wives of Esau. In Genesis 36:2 she is called Adah.
In Genesis 36:3-4,10,13,17 Basemath is the daughter of Ishmael and another of the three wives of Esau. In Genesis 28:9 she is called Mahalath, and is the only one of Esau's wives, whom he took to gain his father Isaac approval, as the other two were both Canaanites as indicated in Genesis 28:8-9. Isaac is not recorded as ever giving approval.