My 16 year old worked last yr. For a couple of months. Can she just filed next yr.?

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.

2018 income can only be reported on the 2018 return.

If there is any taxes withheld, she will most likely get this money back.

She just needs to make sure that she answers,. She Can Be Claimed By someone else (you I assume) when she does her taxes.