"Bent u klaar of niet, mevrouw?"
Translation:Are you ready or not, madam?
I believe "Ik ben klaar" can mean that you have just finished doing* something, but specifically in the sense that what you just finished doing has made you or it completed and prepared for the next thing.
"Klaar" is a loan word from the French "clair." I don't know if "clair" can also have this sense in French, but we do have a somewhat similar (but certainly not identical) usage for "clear" in English. For example, a rocket can be cleared for takeoff, meaning that all is ready for its launch. (See also "security clearance")
*(In English, we would use the gerund "doing" after "just finished" instead of the infinitive "to do.")