Cowles powered the Terps' offense past the Blue Hens with two extra-base hits — one being a homer.
The former Maryland infielder has had a hot start in his professional career in the Houston Astros' farm system.
Right-hander Elliot Zoellner pitched 3 1/3 scoreless innings of relief, but the Terps faltered late.
Weather forced Thursday's game to continue on Friday morning.
Right-hander Hunter Parsons allowed just one run in 7 1/3 innings.
Lee started 4-for-27, but is now hitting a team-best .301.
The Terps swept the Hawkeyes to ensure their season continues.
The Terps can clinch a spot in the Big Ten tournament with a win Saturday.