The security console in the kitchen can be accessed, allowing you to enable security lockdown, locking Mrs. Henderson in the house. Set her robot to "Begin Security Program" mode, and, as it wanders around, disable the "security parameters" data, rendering it unable to determine friend from foe. The robot will also be hostile to you. If you do manage to destroy the robot after it kills Mabel but before deactivating its security mode, you will not be locked in the house, just deactivate the security on the terminal and you can leave.