Rooper told Britain's The Telegraph the two may join each other on the stage again after their sold-out run in London.
"We're hoping to bring it back with her in the U.S.," Rooper said.
"It was amazing" working with Lansbury, she added. "She didn't get any special treatment, she's a grafter. Whenever you feel like you've got a bit of a headache and you can't be bothered, she's almost 90 and she's delivering every day."
The play opened March 18 and ran through June 7 at the West End's Gielgud Theatre.
It was Lansbury's first stage performance in nearly 40 years, Playbill.com reported.