@danilol = I am going to assume this child is a full time student under the age of 24.
1) NEVER comingle her income with yours'. It always requires a separate tax return
2) the fact that she earned money doesn't change the way you complete your tax return. You claim her like you always did
3) The IRS rule is that if soneone's W-2 earnings are less than $12550 (2021) they are not required to file. HOWEVER, if you want to get back the federal withholdings, then you need to file. Same goes for the State (although the earnings minimum may be different). if the earnings are on a 1099-NEC (contractor), then there is a filing requirement beginning at $400 of income.
4) when the daughter completes her tax return, there is a check box asking whether someone else CAN claim here. THat has to be checked for tthe return to be correct
IF she is NOT a student, even if she lives with you and you are paying all her living costs, you cannot claim her on YOUR taxes since she earned more than $4300 (2021). Her filing rquirement is the same, but she doesn't check the box stating someone else CAN claim her,
