Dear,
Anxiety often leads to several physiological reactions in our body. As you mentioned, she is suffering from cancer and is undergoing chemotherapy for the same. She is bound to feel anxious and distressed about it might be resulting in pain and other gastrointestinal issues. Death anxiety is commonly associated with cancer.
Next Steps
Consult a Psychologist or a Psychiatrist who can rule out if she has any psychosomatic illness. If all any such issue exists, appropriate treatment can be initiated.