Did she lock it on purpose? First, you contact her. Ask for the password. If she refuses, you have an attorney contact her regarding committing a cybercrime against your company. File a police report and have her arrested for commiting a cybercrime. She could be arrested and sued for any lost data, lost revenue caused by her locking out the computer. Tell her you will be hiring a computer security firm to recover the password and information at her expense. She could be facing thousands of dollars in cost.
You don't want to access the computer yourself, if she locked it intentionally. You want to file a police report and hire a firm to access it. In case you have court proceedings.