Take a look at the original sentence again:
Lorna did not last long in Mr. Wolcott's busy office,
her long fingernails made accurate typing impossible, and her abrasive
manner scared away too many potential clients.
You wanted to fix it this way:
Lorna did not last long in Mr. Wolcott's busy office
her long fingernails made accurate typing impossible, and her abrasive
manner scared away too many potential clients.
To delete the comma between office and her would cause an equally bad problem, a fused sentence. A fused sentence occurs when you have two main clauses joined with no punctuation whatsoever. Lorna did not last long in Mr. Wolcott's busy office is the first main clause. Her long fingernails made accurate typing impossible is the second main clause. The spot between office and her needs a stronger break than blank space.
You might want to consult the rules for fixing comma splices and fused sentences.
Go back to the sentence to try again.