Called a ex-coworker the c-word.

Hi. I used to work with a co-worker and things went sour quickly. I was pretty close to her at work. After she left her job, I saw a story on her instagram story and then she blocked me. Then I was frustrated and felt she stabbed me in the back and then I wrote her a message and called her the c-word. This happened after she was no longer working here. I regret what I said and shouldn't of said the c-word. If she was still working here, I would be fired on the spot. But since she's not working here anymore and she's a ex-coworker, I'm not sure if I would get fired on the spot? Staff and members at the gym really love me and people say they notice a difference when I'm gone and she took clients from our gym for her own business.