During the process of polishing my novel to query agents, I employed a professional editor. Should I include this information in my query? If so, to what extent?
First, leave me to my delusions that you wrote the book yourself with no help. That way I won't wonder if you can do it again.
Second, even though it's true you had help (beta readers, critique group, caustic comments from the QueryShark perhaps) I don't care how your novel came to be. I only care what it's about.
You don't have enough room in a query to add filigree. Get the plot on the page. Tell me what the book is about. Count it as a good day's work.