Assets like that which get lost or disconnected from the owner are usually turned over to a department in the state government. The term is "escheat".
You can probably find it by googling for "escheat + <state name>" of the states where you or your Mom lived during that time frame. Here is what my state's site looks like:
https://yourmoney.idaho.gov/. Once you get to the state site, you can put in your first and last name and then look at the results.
There are companies that will do this for you but they charge a fee or percentage. I think it's simple enough to do for yourself.
While you're at it, you could look for lost assets of your Mom's as well by putting in her name. Any assets of hers that you found would probably need to go through probate to get distributed (presumably to you and any other heirs or beneficiaries she had).
You could also check with other family members or if you know who served as her executor you could ask them.
If you know where she kept her investment accounts, you could call them and ask if they have a Roth in your name - they'd just need your name, date of birth, and SSN. If you're currently under the age of majority in your state, you may need help from your custodian / parent / guardian.
