Outdoor cat issues, need advice please?

I have had an outdoor cat for 6 years that has never caused any trouble.Now she is really making me angry and I dont know what to do.I recently fixed up some beautiful flower beds near my front door.They have a weed barrier cloth with flowers planted in it and surrounded by red dyed mulch.the cat has decided to use my new flower beds as a litterbox.She is scattering mulch all over my sidewalks and it smells bad.Is there some type of repellent or way to stop this behavior?