Sorry to hear about your mom's passing.
The IRS can seek to recover the amounts owed from her estate but it's not likely that they'll try to pursue the car directly. Because it's a very small estate the windup will hopefully be simple but you'll want to make sure any claims against the estate are addressed properly. You may need the services of an estate attorney.
Evan A. Nielsen is licensed to practice law in California and handles federal tax matters throughout the U.S. The information provided here is for educational purposes only and is not intended as legal advice for a particular matter. This response does not create any attorney-client relationship with the author. For specific advice about your particular situation, please consult an attorney.