Review the original item:
While flirting on the phone with the satellite dish salesman, Rose forgot
about the omelet cooking in the kitchen,
she was surprised when the stovetop fire filled the house with smoke.
You chose the correct way to fix the error:
While flirting on the phone with the satellite dish salesman, Rose forgot
about the omelet cooking in the kitchen,
so she was surprised when the stovetop fire filled the house with
smoke.
Rose forgot about the omelet cooking in the kitchen is a main clause. She was surprised is the second main clause. An excellent way to join these two main clauses is to use a comma and a coordinating conjunction like so.