Not sure what you mean by "put her on my taxes." You cannot file a 2025 tax return until the 2025 tax season is underway in early 2026. If you are able to claim your grandchild as a dependent for 2025, you can do it at that time.
IRS interview to help determine who can be claimed:
https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent
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