I read the title and thought: "Good! She can pull the groceries home from the store behind her bike!"
Then I realized you were going to pull
her in the trailer.
A quick excercise in low speed aerodynamics: if your trailer sides/top fold down flat like my brother's kiddie trailer does, try pulling it (empty) in both configurations. You can easily notice the extra effort just from the bad aero when it's deployed vs stowed, at very low speeds (like 10-15 mph).