How do I get a new tag/registration for Mom's car since she's in nursing home with Alz's?

My own car is broken down and doesn't run. It's still insured, plan to get it fixed as soon as I get extra money. I have been using Mom's car. She's at nursing home due to Alz's Disease. This month will be time for her car to get new tag/registration. Insurance for her car has expired recently. I got a letter that Mom owes property taxes which actually belong to her stepson since we turned over her Life Estate to him months ago via her attorney. I can't drive Mom's car after March if I can't get new tag/registration. I don't plan on selling it as I need it to drive to see Mom at nursing home. I am in Arkansas. Hope someone here will give me an advise. I will get insurance for her car on March 21st when my SSDI comes in. i understand that Tag Agency will not give new tag/registration if she owes property taxes,but it's not hers to pay it.