Humphries is a graduate of Michigan State University, with a degree in fisheries and wildlife, and has completed course work toward her MBA through the University of Wisconsin. She was awarded an honorary Ph.D. in public service from Central Michigan University in December 2004.

She was hired by the DNR Real Estate Division in 1978 as a property specialist to purchase lands for the department. She served in this capacity until 1981, when she was named a resource specialist in the Land and Water Management Division. She began her career in the Wildlife Division later that year as a wildlife habitat biologist at the Shiawassee River State Game Area. She remained in that position until 1986, when she was named a district wildlife biologist in Grand Rapids.

In March 1996, Humphries was appointed assistant to the resource deputy, where she provided oversight and coordination of department-wide programs and operations, and served as a director's representative on special field assignments in Michigan's Lower Peninsula.

She was named acting resource management deputy in May 1997 until her appointment as acting Wildlife Division chief that fall, and subsequently Wildlife Division chief in December 1998.