I'm not sure how you can be bad at being a secretary but let me assure you that it's possible. I'm not sure how it is difficult to answer phones, make photocopies, and check on supplies all day but some people find it tricky. Here are a few completely hypothetical examples. Imagine a secretary who did not know how to save documents on a computer (when asked "What folder are you trying to save it in?" the secretary might reply, "What's a folder?") or a secretary who tied up the phone line talking loudly to her doctor about her recurring poison ivy problem and the steroid cream she needs a refill on. Imagine a secretary who receives personal calls at the expense of business calls, spends 2 hours at lunch, and takes a cigarette break every 30 minutes but refuses to admit that is where she is going (you might be able to tell she is smoking by the smell when she returns or perhaps the leather cigarette case she leaves on her desk). Imagine a secretary who despite being shown 4 or 5 times can still not operate a simple scanner. Imagine a secretary who talks to herself all day long and hangs pictures of cats all over the office. These examples are, as I already stated, completely hypothetical, obviously, because what kind of person would I be if I took advantage of some real secretary's stupidity? A mean person. And I hate mean people.
PS- She might also clip her nails at work and cook smelly cheesy broccoli in the office microwave.