If she is the manager and has a staff why is she working the front counter?

I've never seen a manager hand off a difficult customer to a lower employee. As a customer I would ask to speak to the manager if I wasn't getting service never does the manager ask the co-op student to handle this difficult customer they can't.

Something about your story doesn't add up. You say she is the nicest person but is she good at customer service because those are two different skills.