If she received her green card in 2018, she can file a full year resident return declaring her worldwide income for calendar year 2018. She can use the foreign tax credit to help offset any double taxation.
Or she can file a dual status tax return (part year non resident and part year resident). Her residency starting date would be the first day in 2018 that she was present in the US as a green card holder.
Dual status returns are complicated. She would need to file as married filing separately and would not be able to take the standard deduction, only itemized deductions.
Please see the below publication, page32.
Publication 519
Please let me know if you have questions.
