She could possibly get an increase of amount based on his previous tax returns but I do not believe that an increase can be based on an temporary increase that occured this year…it will not show up on his income yet.
His attorney will need to let the court know that she is voluntarily unemployed and providing that the child is school age, the court can use her previous earnings to compute a salary for him. It was probably never put into the calculations because she did not put it into them. If he signed an agreement for child support and did not argue the point at that time, then there is little that can be done.
I do not know for certain about the adoption and SS but if this were me, I would contact SS and find out about this. This sounds like fraud. If she is receiving money from SS then it should be included as income for her. This may be the only amount used unless, as I said previously, the court takes into account her earning potential.
The child support would be a separate matter to the courts from the divorce and any settlement or agreement issues.