Take another look at the original sentence:
You wanted to fix it this way:
A comma splice occurs whenever you have two main clauses incorrectly joined with just a comma. She saw gold glinting from the breadcrumbs is one main clause. Following it is finally at last, she had found her earring, another main clause. To connect these two main clauses with just a comma between breadcrumbs and finally won't fix the problem, even if you toss in a couple of additional words like at last.
You might want to consult the rules for fixing comma splices and fused sentences.