There's a worksheet in Pub 17 you can go through to see if the daughter did, indeed, provide more than 1/2 of her own support. In the new Pub 17 it's on page 29.

Short version:

1. Daughter's income -- $28k
2. Amount of line 1 used for her own support
3. Expenses for entire household (rent or fair rental value of home if owned, utilities, food, repairs, all other household expenses)
4. Total number of persons in household -- 3
5. Line 3 divided by line 4. This is the daughter's share of household expenses.
6. Daughter's personal expenses (clothing, education, medical, travel, personal, etc.)
7. Add lines 5 and 6. This is the cost of the daughter's support.
8. Line 7 times 50%
9. Is line 2 > line 8? If so, she's NOT a dependent. If not, since she meets the other tests to be a qualifying child (see below), she IS a dependent.

Tests to be a qualifying child: Relationship? Check. Age? Under 24 and full-time student, check. Residency? Check. Joint return? I'm assuming check, though you didn't say.

Pub 17 is your friend. Seriously.