Take a look at the original sentence again:
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 donut and soda.
You chose to fix it the correct way:
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 donut and soda.
A semicolon is always a correct way to join two main clauses that are closely related in meaning. 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.