That one asshole at work

Have you ever thought to yourself Why are some people so miserable in life and strive to destroy a company , Now when this company opened and it was just me and a few other people that had been with this company since the beginning we all got along fine ... until I was promoted and she took it hard. here is her problem. she works a fulltime job an she works here pt , now it has always been that way until I hired better staff and my new staff grew my business up to where we are today, but yet I have this one miserable woman still here. I had to cut her hours down to less than 20 hours as she was being rude and lazy to my customers , and now its gotten so bad that shes mad and is currently bad mouthing me and my good staff to very high end people that spend thousands of dollars in our place , what to do what to do with the asshole that continues talk ? my solution is to fade her away , less hours less days , less time in my business,