It's not if her earned income was at least half of her total income, it's if her earned income is more than half her support. But that's not relevant here. That has to do with whether she is eligible for the American Opportunity Tuition Credit (AOTC or AOC).
You never needed form 8615 because her unearned income is less than $2200. Even if her unearned income is more than $2200, form 8615 is not generated if her taxable income is 0. And, that's the case when her unearned income is taxable scholarship, up to $12,550.
