If she was issued a W-2 for her 2018 wages and had taxes withheld then she should file a tax return to get the taxes refunded.
She is not required to file a tax return if her gross income in 2018 is under $12,000. If her income was from self-employment and was issued a Form 1099-MISC or only cash and the total received was $400 or more she is required to file a tax return for the self-employment.
Income earned in 2018 can only be reported on a 2018 tax return, not on a future tax return.
