Who was Rachel's servant that she gave to Jacob?

Answer: Bilhah

Rachel gave Jacob her servant Bilhah to bear children for her.

“Then she said, “Here is my maidservant Bilhah. Sleep with her, that she may bear children for me, so that through her I too can build a family.” So Rachel gave Jacob her servant Bilhah as a wife, and he slept with her,”— Genesis 30:3-4 (BSB)