In First Chronicles 1:32-33, she is called Abraham's "concubine" (pilegeš))
According to Jewish tradition, she was a descendant of Noah's son Japheth, but some Jewish Rabbis think that she is the same person as Hagar.
For being such an important figure, we know next to nothing about her.
Isaac was not the only son of Abraham, but he was the only heir and his father gave him everything. Because of this, he is called the only son of Abraham. All the others were treated as step children. God promised him a son through Sarah.