To change the question to a negative sentence, The sentence can be written as "Hasn't she told them to wash their uniforms?"
To transform the directive statement "She has told them to wash their uniforms" into a negative question, you can frame it as an inquiry about the absence of an action. Consider the negative aspect by asking if the action hasn't been completed. For instance:
"Hasn't she told them to wash their uniforms?"
This phrasing implies doubt or uncertainty about whether the instruction to wash uniforms has been given. The use of "hasn't" creates a negative form, and by framing it as a question, it prompts the listener to provide information or clarification.
This construction maintains the context of the original statement while introducing an element of questioning or skepticism regarding whether the directive has been conveyed.