What exactly was done wrong? How do you know it's the wrong amount? How does she know her SSD was screwed up? What is it that she thinks Social Security needs to do?

Generally the only thing that reduces a Social Security disability benefit is receipt of worker's compensation (including a settlement which can be prorated into the future) or public disability benefits. There can be garnishment for unpaid child support or overpayment recovery. But other than that, the computation to determine the monthly amount of Social Security Disability is pretty straightforward and not subject to error since it is based on the earnings record. Does she disagree with her earnings record?

Now SSI, Supplemental Security Income, can change for a variety of reasons; living arrangements, other sources of income, help from others, etc. SSI can legally go up and down and change every month.

I have no idea what she should do because I don't understand the problem. I suggest talking to the office in person with the evidence she has that shows she is being paid incorrectly.