Dependents

You cannot claim your GF as a dependent unless she lives with you for the entire year and has less than $4700 of income --not counting Social Security.  If she has not moved in yet, then you will not be able to claim her for 2024, since it is already late March.

CREDIT FOR OTHER DEPENDENTS

https://ttlc.intuit.com/questions/4499708-what-is-the-500-credit-for-other-dependents-family-tax-credit

I should had made it known. She hadn't yet moved in. But if she moves in in April, 2024. Is that when the time begins that I could claim her for 2025?

No.   If she was not moved in by January 1, 2024, you cannot claim her for tax year 2024.   You cannot claim her when you prepare your 2024 tax return next year in 2025, because she will not have lived with you for the entire twelve months of 2024.   

No, the rules state that she must live with you the entire year, So, 2024 has already gone by.

You may be able to claim her as a dependent on your 2025 taxes, but you will not file them until 2026.

Bottom line ... Don't have her move in just to get a tax break!

To qualify her as a dependent  

• Your partner must have lived with you for the entire calendar year 
• She must have listed your home as her official residence for the full year. 
• Her gross income must be less than $4,700 for tax year 2023.(Will probably be higher in 2025)
• She can not be claimed by anyone else as a dependent.

For more details please see: Can I Claim a Boyfriend/Girlfriend as a Dependent on Income Taxes?