It depends on if she files a joint return with her spouse and whether you meet all of the requirements to claim her.
If she files married filing separately OR if she files a joint return with her spouse and it is only for the purpose of getting back withheld taxes or estimated taxes, then you can claim her as long as you meet all of the requirements.
If she files jointly for any other reason, you would not be able to claim her. Please refer to pages 12-13 of Pub 501 under the heading, "joint return test". https://www.irs.gov/pub/irs-pdf/p501.pdf.
Additionally, please refer to the chart on page
12 of pub 501 to see if you meet the requirements to claim your child as a
dependent. https://www.irs.gov/pub/irs-pdf/p501.pdf.
