You cannot just deduct the money you are giving to your sister. Gifts to individuals are not deductible. You might be able to claim her as a qualified relative if you claim her as a dependent and then you would get the $500 credit for other dependents.
https://ttlc.intuit.com/questions/2892814-does-a-dependent-have-to-live-with-me
CREDIT FOR OTHER DEPENDENTS
https://ttlc.intuit.com/questions/4499708-what-is-the-500-credit-for-other-dependents-family-tax-cre...
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