There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, a relationship test and residence test. Only a QC qualifies a taxpayer for the Earned Income Credit and the Child Tax Credit (must be under 17).
Since she is under 19, she can be your QC, as long as she lived with you more than half the year.
It doesn't matter how much she earned. What matters is how much she spent on support. Money she put into savings does not count as support he spent on her self.
The support value of the home, provided by the parent, is the fair market rental value of the home plus utilities & other expenses divided by the number of occupants.
