Take another look at the original sentence:
You wanted to fix it this way:
To delete the comma between breadcrumbs and finally would cause an equally bad problem, a fused sentence. A fused sentence occurs when you have two main clauses joined with no punctuation whatsoever. She saw gold glinting from the breadcrumbs is the first main clause. Finally, she had found her earring is the second main clause. The spot between breadcrumbs and finally needs a stronger break than blank space.
You might want to consult the rules for fixing comma splices and fused sentences.