The purpose of this study is to find out if the study drug, Obinutuzumab, is effective in achieving a complete renal response for adolescents with active class III or IV lupus nephritis. Researchers will also be testing how the body processes a drug by measuring how quickly the drug is absorbed by the body, how quickly it is broken down by the body, and how long it remains in the body (pharmacokinetics). Subjects will be asked to come into the Rheumatology clinic for blood, hepatitis and pregnancy testing, physical exam, an electrocardiogram (ECG), questionnaire completion, chest x-ray, MMF/oral corticosteroid use, medical record review, optional genetic testing, and administration of study drug. Obinutuzumab is administered as an infusion 5 times over the course of the study.