I am sorry for your loss.
An inheritance is not generally taxable to the heirs unless some sort of retirement account is involved.
Otherwise, an income tax return for the estate (Form1041) is not required to be filed unless the estate has gross income of $600 or more.
See https://www.irs.gov/instructions/i1041#en_US_2021_publink1000285942
Note that if you are her personal representative, you may need to file a final individual income tax return for her.
See https://www.irs.gov/publications/p559#en_US_2021_publink100099488
