Niebla received an associate of arts degree from Fullerton Junior College in 1965 and a BS in zoology and chemistry from the University of Arizona in 1967. She taught special education in California for three years before returning to the University of Arizona, where she received a PhD in soil chemistry in 1979. Niebla took a job at the Western Archaeological Center, where she worked on maintaining historic adobe buildings and ecosystems in national parks. In 1984 Niebla joined the Environmental Protection Agency (EPA) and wrote regulations on the use of sludge made from decomposed garbage on agricultural land.
In 1989 Niebla became national coordinator for global change research in the Forest Service, a division of the U.S. Department of Agriculture. She manages the science research program on global change in forests.