I am Head of Household, one dependent over 21 years old. She received some interest income from her bank CD, separate from mine. Do I add her Interest Income to mine?

Q Do I add her Interest Income to mine?

A.   If the amount is less than $1300, it does not need to be reported at all.

If more than $1300, yes , but not exactly. You do not add her interest to yours. Instead you make a separate entry for her income. 

 If her only income is from interest and dividends, Alaska PFD or capital gains distributions shown on a 1099-DIV, there is a provision for entering it on your return, using form 8814. Enter at Less common income / Child's income.

About dependent's income (in general):

You do not normally report his/her income on your return (see exception above). If it has to be reported, at all, it goes on his own return. If your dependent child is under age 19 (or under 24 if a full time student), he or she must file a tax return for 2024 if he had any of the following:

1.          Total income (wages, salaries, taxable scholarship etc.) of more than $14,600 ($13,850 for2023).
2.          Unearned income (interest, dividends, capital gains, unemployment, taxable portion of 529 distribution) of more than $1300 ($1250 for 2023). 
3.          Unearned income over $450 and gross income of more than $1300.
4.          Household employee income (e.g. baby sitting, lawn mowing) over $2600 ($14,600 if under age 18)
5.          Other self employment income over $432, including money on a form 1099-NEC

Even if he had less, he is allowed to file if he needs to get back income tax withholding. He cannot get back social security or Medicare tax withholding.

In TurboTax, he indicates that somebody else can claim him as a dependent, at the personal information section.