You would treat the refund that same as your mother would have. If you took the standard deduction on her final tax return, it is not taxable and you needn't report it.
If you itemized, you need to claim the amount that pushed her itemized amount over the standard amount.
It would be entered under "Income", Other Common Income, tax refunds
According to the IRS:
"All income the decedent would have received had death not occurred that wasn't properly includible on the final return, discussed earlier, is income in respect of a decedent."
"Character of income.
The character of the income you receive in respect of a decedent remains the same as it would have been to the decedent if he or she were alive. If the income would have been a capital gain to the decedent, it will be a capital gain to you."
Sorry for your loss.
IRS PUB 559
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