When you give another person a power of attorney, she becomes your agent and can act on your behalf in the matters you authorize in the power of attorney document. You, the principal, have the right to revoke your agent's powers at any time and for any reason. Revoke your agent's powers in writing as soon as you make the decision to prevent her from continuing to act on your behalf.
Exact revocation procedures vary by state, but typically, you must deliver a written notice to your agent. In the notice, clearly identify the power of attorney document that you are revoking, including its date and the agent's identity. Provide a copy of the notice to any person or entity, such as your bank, that has the original power of attorney document on file. Third parties may continue to allow your agent to act on your behalf if you don't deliver formal notice of the revocation in a timely manner.