She just might not beable to handle her job. It happens to some people. Once my wife had our first child is was really over for her. She just couldn't do anything but work and sleep. She was totally useless. New job solved the problem.
Look, get her hormones tested by a qualified endocrinologist. If everything in that department is okay then the next step is to think about counseling. She's a young woman, just throwing drugs at her is going to create problems. You want to definitively rule out health problems and really know WHAT's going on. If it's not physical/hormonal, then the psyche needs to be looked at.
Could be the pill....it can kill the sex drive in women.....have her talk to her Dr. to see if there is a "real" reason besides just not interested anymore