Chronic Fatigue Syndrome: Given the one-month duration of fatigue and body aches without a clear infectious cause (mono viral panel negative), and the presence of toxoplasma IgG positive (indicating past infection) but negative IgM (indicating no current infection), chronic fatigue syndrome is a plausible diagnosis. The lack of specific symptoms pointing towards another condition also supports this consideration.

Fibromyalgia: This condition is characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood issues. The absence of a specific viral or bacterial cause for her symptoms makes fibromyalgia a consideration.
Depression or Anxiety: These conditions can manifest with physical symptoms such as fatigue and body aches. The psychological impact of chronic illness or stress could be contributing factors.
Hypothyroidism: Although not directly related to the toxoplasma test results, hypothyroidism can cause fatigue, body aches, and other non-specific symptoms. It's a common condition that should be considered in the differential diagnosis of fatigue.

Lymphoma: Although less likely, lymphoma can present with non-specific symptoms such as fatigue and body aches. Given the potential severity of this diagnosis, it's crucial to consider it, especially if other symptoms like weight loss or night sweats are present.
Systemic Lupus Erythematosus (SLE): SLE is an autoimmune disease that can cause a wide range of symptoms, including fatigue, body aches, and can be associated with positive toxoplasma IgG due to the immune system's dysregulation. Missing this diagnosis could lead to significant morbidity.
HIV: HIV infection can present with non-specific symptoms such as fatigue and body aches. Given the potential for severe consequences if left untreated, HIV testing should be considered, especially if risk factors are present.

Toxoplasmosis Reactivation: Although the patient has a positive toxoplasma IgG and negative IgM, suggesting past infection rather than current, in immunocompromised individuals, toxoplasmosis can reactivate. This would be a rare consideration unless the patient has a known immunocompromised state.
Other Chronic Infections: Such as brucellosis, or less common viral infections could potentially cause these symptoms, though they would be less likely without specific risk factors or exposures.