If it is just a bank account.. no you cannot be sued. but they could take all the money for her care so do not put any of your own $$ in it.
Now if she asks to put you on the title to her car... be careful!
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No, in general, you can not be sued for being a bank account holder. The bank account is merely an asset, and has no liability associated with it; hence, you can have your name on the bank account without incurring any liability. Alternatively, you can also have your mother execute a Durable Power of Attorney, granting you the authority to making financial decisions on her behalf. You can also setup a living trust for your mother, with you as a trustee, and open bank accounts in the name of the trust; you will then have the ability to manage the assets of the trust for the benefit of your mother and any other beneficiaries whom she names.