Grandchild becoming my dependant

You have not provided us with enough information.  Who did the child live with?   When did she begin to live with you---or did she?

IRS interview to help determine who can be claimed:

https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent

https://ttlc.intuit.com/questions/3113432-who-can-i-claim-as-my-dependent  

Prior to living with me in 2024 she was living with her Mother (my daughter) she moved out of state and gave me guardianship when she moved. My granddaughter started to live with me in January of 2024.

If your grandchild has been living with you since January of 2024, then you should be able to claim her as your dependent.   Depending on her age    (and your own income)  you may get child-related credits such as the child tax credit, earned income credit, or the childcare credit.  And you may be able to file as Head of Household, which will make less of your income taxable.

Am I Head of Household?

https://ttlc.intuit.com/questions/1894553-do-i-qualify-for-head-of-household

https://ttlc.intuit.com/questions/2900097-what-is-a-qualifying-person-for-head-of-household

If you qualify as Head of Household, when you enter your marital status (single or married filing separately) into MyInfo, and then enter your qualifying dependent, TurboTax will offer HOH as your filing status.

WHO CAN I CLAIM AS A DEPENDENT?

You can claim a child, relative, friend, or fiancé (etc.) as a dependent on your 2024 tax return as long as they meet the following requirements:

Qualifying child

• They're related to you.
• They aren't claimed as a dependent by someone else.
• They're a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They're under the age of 19 (or 24 for full-time students).
• No age limit for permanently and totally disabled children.
• They lived with you for more than half the year (exceptions apply).
• They didn't provide more than half of their own support for the year.

Qualifying relative

• They don't have to be related to you (despite the name).
• They aren't claimed as a dependent by someone else.
• They're a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They lived with you the entire year (exceptions apply).
• They made less than $5050 in 2024.
• You provided more than half of their financial support.

When you add someone as a dependent, we'll ask a series of questions to make sure you can claim them. There may be other tax benefits you can get when you claim a dependent.

To claim a grandchild as your dependent

When you enter the child’s name in My Info, you will be asked “What’s your relationship to  [child’s name]?”  

           Choose “another person”

            a drop down menu will appear that lets you choose grandchild