If your friend is on SSI, not Disability Social Security, she would have a caseworker locally who is responsible for recertification of her case regularly. This is an income based program, and they require regular verification of all expenses and sources of income in each case. And they are used to working with people who are somewhat limited in their ability to understand exactly what is happening.
It may turn out when you get more deeply involved that what your friend is being required to "go to the office and make regular payments" on isn't exactly what she believed it was. Could it be that there are some sort of sanctions, that she may be repaying some sort of overpayment or something? If her children were adopted by someone else, I wonder if she had an attorney at all in this process. Social services should be a first source of information but then, of course, the legal aid program works with social services clients frequently.
I'd begin by having her call her case manager and ask exactly what she is receiving, exactly what this payment she makes is, etc. Ask her to write down the information they give her. Sometimes when one gets involved, we find that the descriptions and explanations that people have of their economic situations are clearer than they first sound.