Dear Ms Hewitt,
I would like to thank you about your interest in our company. We had read your CV with attention but, unfornatunately, your application for the post of Junior Marketing Manager cannot receive a positive answer. You have a lot of skills for the post, but we had had to considered your lack of experience in marketing.
I hope you will find soon a post in what you are looking for with another company.
My text is rather short but let's say it will do for now. ^^