For the tax year 2017, you can claim your sister as a dependent if she lived with you more than half the nights of the year, is under age 19 or is a full time student under age 24, did not provide more than half her own support, and if you are older than she is.
Her parent can't claim her if the child did not live with the parent (live in the same home as the parent) more than half the nights of the year.
