difference between non-hodgkin's lymphoma and colon cancer

My mother, aged 71, was diagnosed with a high grade B-cell non-hodgkin's lymphoma of the G.I. tract. She died from it very quickly-about 37 days from the time I took her into the hospital.The doctors said it was rare. Actually, 2 years before her death she presented with a bloody pericardial effusion in her chest. She never had swollen lymph nodes, and after a bone marrow biopsy and a peridardial window, it was determined she did not have cancer, although lymphoma was talked about.The fluid from her chest was tested and there were suspicious cells in the fluid but not enough to make a definitive diagnosis. For the next two years I saw her go downhill, and she was always sick to her stomach and complained of constipation.She was not monitored on a regular basis. Her gastroenterologist would just give her Prilosec or Prevacid for the stomach problems. When the diagnosis finally came, she had had a colonoscopy and a CT scan, and an upper endoscopy, and the doctor had found lymphatic tissue in her colon. They tried one chemotherapy treatment, but she threw a pulmonary embolism and died one week later.I am confused about the type of cancer she had. Was it non-hodgkin's that started in her colon, or was it colon cancer that caused the non-hodgkin's or are the two not even related. I am her only child. Should I be screened regularly for colon cancer. I just had a colonoscopy anyway at the age of 48, about 5 months ago, and it was normal. My mother also had been diagnosed with h. pylori infection, and I had it also, and was treated with antibiotics. I had the upper G.I. and no lymphocytes were found. My mother also had lung cancer-adenocarcinoma-ten years before her death. The doctor got it all in surgery-she had no chemo after. By the way, she never smoked, but she had jobs in factories, especially one where they made talc, so I don't know what she breathed in.Could you please be so kind as to clear up this confusion for me. Thank you. Also, can cancer lay dormant in your body before it is found?