Can I get special tax forgiveness for a child I claim my niece every year although she is not mine I have a court order in place until she is 18 can I check yes?

Yes, you can claim her as a dependent.

There are two ways a person can be claimed as a dependent.  This can apply to you.

• They are not claimed as dependent by anyone else.
• They are US citizens.
• They live with you? They must live at your residence all year.
• They made less than $4,400 in 2022? 
• You must provide more than half of your relative’s total support each year.

If she lives with you, for more than half the year, she is your "qualifying child" dependent, whether you call her your foster child or niece. 

If she is your foster child, your are allowed to check "my child". See the list on that screen.

If you check "someone else I support", niece/nephew will be on the drop down list.