The marital status for the FAFSA is as of the date of filing. If this mother divorces or is separated from the stepfather the day the FAFSA is filed for the 2019-2020 school year, she would only include HER income from 2017, not the step parent.
It doesn’t matter if they were married in 2017. What matters is if they are divorced or separated the day the FAFSA is filed. If so…only the custodial parent income is listed.