Muscle weakness affects the muscular system (muscles are in the muscular system) , stomach pain affects the digestive system (stomach is a part of the digestive system), and coughing affects the respiratory system (coughing hinders the ability to breathe properly).
The answer is Iron, this is the important mineral that she
needs to obtain as this will help her in her ways to cardiovascular fitness as
this mineral helps the hemoglobin to build in her body and for her t be able to
get enough nutrients.