Trouper vs. trooper

When using the phrase "He's a real tro*per," do you use the word "trooper" or "trouper." They would both seem to make sense in different contexts, but I have an editor who is insisting it's one way only. Any thoughts?
Thanks.

Trooper is a state policeman or cavalry officer. Trouper is taken from troupe, group of performers. I think the phrase "she's a trouper" would be "trouper."

From the Associated Press Stylebook: troop, troops, troupe -- A troop is a group of people or animals. Troops means several such groups, particularly groups of soldiers. Use troupe only for ensembles of actors, dancers, singers, etc.