Additional income taxes to be paid

Your question doesn't make any sense ... did you fail to report the income on the return so they sent you a CP2000 notice ?   

the IRS does not tax inheritances per se, but if you receive something like an IRA or stock and cash it in you will owe taxes not because you inherited it but because you cash it in. we can't provide any more help because you provided no details as to what she inherited and what was done with it.