 This pilot phase I trial studies the side effects of atezolizumab, gemcitabine, oxaliplatin, and rituximab and to see how well they work in treating patients with transformed diffuse large B-cell lymphoma that has come back or does not respond to treatment. Monoclonal antibodies, such as atezolizumab, may interfere with the ability of cancer cells to grow and spread. Drugs used in chemotherapy, such as gemcitabine, oxaliplatin, and rituximab, work in different ways to stop the growth of cancer cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving atezolizumab, gemcitabine, oxaliplatin, and rituximab may work better in treating patients with transformed diffuse large B-cell lymphoma. 