The symptoms presented could be associated with multiple conditions. Because she has been experiencing these symptoms for an extended period of time ( a month), this would eliminate many of the known causes.
Other conditions which may contribute to symptoms of nausea, extreme fatigue, night sweats and may present with further long-term symptoms may include; fibromyalgia syndrome, myalgic encephalomyelitis, and chronic mononucleosis, Lyme disease, acute bacterial or viral conditions, and others. Although these illnesses may present with a primary symptom other than fatigue, chronic fatigue is commonly associated with all of them. Chronic fatigue as a symptoms may be related to CFS (chronic fatigue syndrome), which also presents with nausea, and night sweats, and seems to be on the rise. CFS is a complex disorder, which is characterized by the increase with fatigue, where rest does not improve this symptom. There are other symptoms which may be associated with this syndrome, including weakness, muscle aches/pains, impaired concentration and/or memory, insomnia and other's, as these may further develop over time. There aren't any specified diagnostic tests to determine/diagnose CFS, as diagnosis is primarily based on the prolonged symptoms associated with this. treatment is based on the treatment of the underlying symptoms. It is recognized that early detection and treatment is vital with this, as early intervention is responsible for a more favorable outcome. Studies indicate that the longer one waits to be properly diagnosed, (if this is the case), the more complicated the treatment and illness becomes.
I would consider having her re-visit her primary care physician for further evaluation and testing/studies. He/she may obtain the necessary tests in order to rule out many of the above listed associated conditions. This may have to be approached in a "process of elimination" method, to determine the precise cause/diagnosis, in order to treat as necessary. You may also obtain a referral is need be for further studies if indicated by physician.
I will also include a website below on further reading regarding this;
Chronic Fatigue Syndrome (CFS) - Fibromyalgia & Fatigue Centers
If you have any further questions or concerns, please do not hesitate to ask.