Fiances Ex Girlfriend

Katie
So how do i tell my fiances ex to fuck off nicely... i have told her many times before to leave him alone to stop txting him, talking to him, and just move on. She messaged him when she found out we were engaged, and then again when she found out we are expecting again. And many other times, shes even tried being friends with me, then blocked me after a drunk txt to him asking to fuck. And again she txt him today on his birthday (She aborted their child 4 years ago before telling him she was even pregnant and then told him she did it because he wasnt a good enough father) and is saying he will always be apart of her because of that.