Does social security pay back pay in a lump sum or in installments.?

My sister in law was approved for Social Security disability in June and received her $16,000 back pay in a lump sum. Sometimes it depends on what the disability is. I worked for social services and had a few clients that were approved for disability related to drug or alcohol complications. These people did not get lump sum payments, but installments and some of them were required to have a payee.