Contact the entity that is handling your mothers IRA. Explain the situation. They will ask you for some verification and you will have to fill out some forms. This will take awhile. Once the entity established who the funds legally belong to- they will disburse them. Keep all of this paperwork, including photocopies of the check, copies of any emails, etc. You will need to address this when you file her 2017 return. Because she died so late in the year, your best option is to do two things simultaneously-deal with the entity that handles the IRA and contact the IRS. Hopefully you can get the funds at least "assigned" before you have to file your mothers return so that the disbursement can be noted.
