Take another look at the original sentence:
You wanted to fix it this way:
To delete the comma between loudly and she would cause an equally bad problem, a fused sentence. A fused sentence occurs when you have two main clauses joined with no punctuation whatsoever. Poor Paola listened to her stomach rumbling loudly is the first main clause. She would have to wait twenty more minutes is the second main clause. The spot between loudly and she needs a stronger break than blank space.
You might want to consult the rules for fixing comma splices and fused sentences.