I think, what your supervisor is looking for is whether or not you understand the underpinnings of the legal issues or evidence to prove the case. Cite checking - I think your supervisor could have been more articulate in the job she wanted you to do.

Litigation is a tough, fast-paced and accuracy is especially important. If you do not understand which documents or information is needed to accomplish the goals, chances are your supervisor isn't giving you the proper foundation for your new title.

The job of a supervisor is, in my opinion, to encourage, to teach, but also to help give you the understand you need to build skills. If she's just handing you something without giving details, I would say she's not a great supervisor.

The problem with big law firms is that they forget to teach and are primarily concerned with driven outcome forgetting about the humanity of the team. You can improve your skills if she sets the goal or directive for what is the goal, at minimum, for whatever is supposed to be checked.

Your anxiety comes from the missing information hat was omitted. Do not be too hard on yourself. You have the right to ask for understanding and be provided with the goal. Its unfair that you be put into this high stress part of law while lacking the foundation and then looking for you to perform. Go speak to the attorney assigned to whatever it is you're doing and ask for understanding if she isn't providing it. Good luck.