Hi! To claim a child as a dependent, as of December 31, 2017, they would have to be less than 19, or a "student" less than 24. If she was 24 at all during the year 2017, you wouldn't be able to claim her as a dependent child. You may be able to claim her as a different category of dependent, which the IRS has a step by step walkthrough to see if she what she could qualify as:
https://www.irs.gov/help/ita/whom-may-i-claim-as-a-dependent
Hope this helps!
