@global77
Use the link from the IRS provided to you and read the criteria for claiming a dependent. You still have not told us her age---only that she is "past 18." A full-time student under the age of 24 can be claimed as a qualified child. She is not limited by the $4300 income amount. She can earn more and still be considered a qualified child if she is a full-time student under the age of 24.
The rule is if the person CAN be claimed then they are supposed to say that on their own tax return. It is not a matter of choice.
If your daughter was a full-time student UNDER the age of 24 at the end of 2020 then she can still be claimed as a dependent on your joint tax return. That means she can still file her own tax return but she must say that she can be claimed as someone else's dependent. She is not eligible to receive stimulus checks. The person (or the couple) who can claim her as a dependent can get the 3rd stimulus check for claiming her, and will get the $500 credit for other dependents. And the education credits go on the return of the person who claims her as a dependent.
You say she had self-employment income. That means she will be required to file a return if she earned even $400, and she will need to pay self-employment tax for Social Security and Medicare, as well as ordinary income tax--depending on how much she earned.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
