This student said in the OP that her EFC was $0. It can’t get lower than that!
Medicaid doesn’t give any income per month. Are you talking about social security?
Regardless…your parent can file a tax return with whatever income from whatever source.
Whether they filed during a specific tax year or not, you (and parents) need to enter 2016 income information on the 2018-2019 FAFSA. After submitting the FAFSA, inquire with your school’s Financial Aid Office about a Special Circumstance Appeal, if income has decreased significantly since 2016. The ‘professional judgement of income’ is with their office alone.
Thank you!