When did your mother-in-law die? If it was in 2020 or later, the inherited IRA rules have changed substantially. There are no required distributions, the only requirement is to withdraw all the money and close the account within 10 years.
The previous rule which said the beneficiary could keep the IRA and withdraw the amount over their lifetime, taking an RMD each year, only applies to accounts where the owner died in 2019 or earlier.
