This phase II trial studies the effect of polatuzumab vedotin, rituximab, ifosfamide, carboplatin, and etoposide as initial salvage therapy in treating patients with diffuse large B-cell lymphoma that has come back (relapsed) or does not respond to treatment (refractory). Polatuzumab vedotin is a monoclonal antibody, polatuzumab, linked to a toxic agent called vedotin. Polatuzumab attaches to CD79b positive cancer cells in a targeted way and delivers vedotin to kill them. Rituximab is a monoclonal antibody that may interfere with the ability of cancer cells to grow and spread. Chemotherapy drugs, such as ifosfamide, carboplatin, and etoposide, 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 chemotherapy with immunotherapy may kill more cancer cells in patients with diffuse large B-cell lymphoma.