If consigner for a vendor mall opened in dec 2024 but receive first income in 2025, does she file in 2024 or 2025?

If you received the sales proceeds only in 2025, then you'll report it on your 2025 tax return.

If she did not receive any income in 2024 then she does not have anything to file for that year. Her income received in 2025 will be reported for that year.