If she was 23 or younger as of 12/31/2016, and the situation is as you describe, and she didn't file a joint return with someone else, you can claim her. If she was 24 or older on that date, you could claim her only if her own gross income was less than $4050.
If you can legitimately claim her, you should print your return and mail it. That's because if her return is already in the IRS system, yours will be rejected if you e-file.
And if you can claim her, she needs to file an amended return indicating that someone else can claim her.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
