No, individuals are not liable for the actions of others unless they somehow take on that responsibility, for instance becoming their guardian or conservator. However, it may be possible to notify your state motor vehicle licensing bureau that your mother should no longer be driving.
Harry S. Margolis practices elder law, estate, and special needs planning in Boston and Wellesley, Massachusetts. He is the founder of ElderLawAnswers.com and answers consumer questions about estate planning issues here and at AskHarry.info.