I work for a company the processes financial aid applications for schools, not students. The parents do not have to file taxes if they do not have income levels that require them to do so. However, you can't live on ';nothing'; so they are going to be asked how they survive, money has to come from somewhere. They have to show any income or help received on the FAFSA regardless of it's source. Welfare benefits go in a special section. If Grandma pays their rent it goes in a different section, etc.
It's all explained at the following link.How do you file income taxes if your parent is unemployed?
You can file a Form 1040-EZ with the income they do receive, if any, included.
If they don't have enough income to be requried to file, there is no need for them to file.
You don't file tax returns to get grants.
If she's been drawing unemployment, she may need to file anyway as unemployment benefits are taxable.
If she is living with her husband, they file jointly otherwise she would state ';not required to file'; on the grant application.