Hello JA Customer,
In the United States, gift tax (if and when it ever becomes due) is paid by the donor of the gift and not by the recipient. And even US citizens do not pay gift tax until they have exceed their lifetime allowance in non taxable gifts which is currently $1 million. If your sister is not a US citizen, then even this $1 million lifetime limit does not apply. She can give you as much as she ever wants to without ever owing gift tax.
Neither of you are required to report anything unless you would receive a gift from her which exceed the amount of $100,000 in any one tax year. If she ever gives you $100,000 or more as a gift in any one year, then you must file a separate report with the IRS to report the gift on Form 3520. This is required of any gift you receive from a foreign source that exceeds $100,000 in one year's time. There is no tax due with this form. It is strictly for informational purposes only and is really for your own protection so you have a clear record of reporting where this money came from.
If she gives you less than $100,000 in any one year, neither of you are required to file any reports or claim this money anywhere on your tax return.
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Thank you JA Customer