Gross Income Test for a Qualifying Relative Dependent: "Gross Income is all . . . that isn't exempt from tax." Is that 1040 Line 9 Total, 11 AGI, or 15 Taxable Income?

My Daughter turned 24 in 2023, a full-time Graduate student, I provide nearly all of her financial Support, she does have a part-time job, and by any common-sense definition she is my Dependent.  However, her Age disqualifies her as a Qualifying Child so I am trying for Qualifying Relative. If Gross income is defined as "that isn't exempt from tax" do I use Line 9 Total Income, Line 11 AGI, Line 15 Taxable Income.  It seems like it should be Line 15.