US taxpayers never pay tax on gifts received.
US banking security laws require all transactions of more than $10,000 be reported to the treasury department. This is largely to prevent and detect money laundering, and does not necessarily impose a tax burden. If your mother transfers money that she owns from a foreign account to a US account, that would never be taxable in the US because she is just moving her own money around. However, the transaction will be reported routinely. Beware that if she were to make several small transactions under $10,000 each to avoid the reporting requirement, this can constitute a separate crime called “structuring”, even if the ultimate purpose of the transfers is completely legal.
