Do I need to file taxes - Social Security, Overseas Rental

My mother is in her 70's (age) and receives social security income. She has rental properties overseas and in 2021 received approximately $4,000 rental income from them. That was her only source of additional income. Since this amount is less than the standard deduction, do I still need to file taxes for her? I started and see schedule E but then this question came to mind. I can't seem to get a clear answer with lots of google searching. Thanks in advance!