Review the original item:
Susan ducked when she saw Professor Hayden walk into Tito's Taco
Palace,
unfortunately, a burrito was not big enough to hide behind, so poor
Susan had to explain why she had missed class again.
You wanted to fix it this way:
Susan ducked when she saw Professor Hayden walk into Tito's Taco
Palace unfortunately, a burrito was not big
enough to hide behind, so poor Susan had to explain why she had missed class
again.
To delete the comma between Palace and unfortunately would cause an equally bad problem, a fused sentence. A fused sentence occurs when you have two complete sentences joined with no punctuation whatsoever. Susan ducked ... begins a complete sentence. Unfortunately, a burrito was not big enough ... starts the next complete sentence.
The spot between Palace and unfortunately needs a stronger break than blank space.
You might want to consult the rules for fixing comma splices and fused sentences.