She would be considered a dual status alien for 2025. When she meets the Substantial Presence Test after 183 days she will be considered a US Resident. This would require her to file a 1040NR for the first 183 days and a 1040 for the rest of the year.
However, since you are married and you are a US Resident, she can file as a US resident for tax purposes for the entire year if you choose to file a joint return.
Generally, no. A J-2 Visa holder does not qualify for an exemption.
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