My mom has been diagnosed with non small cell lung cancer. she has been vomiting everything she eats and cannot keep anything down. what is causing the vomiting ?

Several reasons: Vomiting can occur due to several reasons which may includes gastric outlet obstruction, chemotherapy, radiation therapy, viral infections, brain lesions etc. Please talk your physician as this is a serious problem that needs to be addressed.

Unknown: There is no way to answer that without knowing what the stage is and whether she is currently under therapy.