Review the original item:
Poor Paola listened to her stomach rumbling loudly,
she would have to wait twenty more minutes before she could dash
to the cafeteria for a quick doughnut and soda.
You wanted to fix it this way:
Poor Paola listened to her stomach rumbling loudly,
so she would have to wait twenty more minutes before she could dash
to the cafeteria for a quick doughnut and soda.
Although a comma and a coordinating conjunction like so can legally connect two main clauses, this correction method will not work in the example above.
The problem is that so, a coordinating conjunction that shows result, does not join the two main clauses logically. Paola is not waiting to eat because her stomach is rumbling loudly.
You might want to consult the rules for fixing comma splices and fused sentences.