Get your taxes done using TurboTax

My daughter will be earning $6K this year which is under the federal and state limits of income required to file, so she will not owe the IRS any money. But, she had a tax liability of $107 last year. Is there any penalty or is it illegal to file exempt this year since she wont owe any money but she had a tax liability last year? I can't understand what that rule is for.