Tuberculosis is a chronic infection that requires longer period of treatment. The decreased appetite and the less weight then expected are often seen in tuberculosis. Treating the tuberculosis will return the appetite in time, thus increasing the weight, too.
You might also visit your doctor in order to check for parasitic infections. Parasitic infections can be one of the causes of malnutrition that is easily treatable.
Additional supplements with vitamins and minerals might be helpful to increase the appetite and to substitute the one she misses because of the lower food intake.