can i claim my grandchild as a dependent if her mom claimed her but they both live with me. I provide all the lodging expenses for them and she has already claimed her?

The child's SSN can only be entered on one tax return, so if you claim her, your return will be rejected.   The real issue is who supports the child.    If you are the one supporting your daughter and her child,  you may be able to claim both of them as dependents on your tax return.   Your daughter would have to amend her own return, of course.

• What does "financially support another person" mean?

   

  IRS interview to help determine who can be claimed:

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

   

   

   

  WHO CAN I CLAIM AS A DEPENDENT?

   

  You can claim a child, relative, friend, or fiancé (etc.) as a dependent on your 2025 taxes 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 $5200 in 2025 (not counting Social Security)
      • You provided more than half of their financial support