Unless your mother has already made reportable gifts of more than $11,580,000, then no gift tax will be owed. You have to file Form 709 so the IRS can keep track of lifetime gifts.
From What Is the Lifetime Gift Tax Exemption?:
Starting in 2020, the lifetime gift tax exemption is $11.58 million. This means that you can give up to $11.58 million in gifts over the course of your lifetime without ever having to pay gift tax on it.
