How do you feel about bumping into your partners ex?

My boyfriends ex is a pain in the arse. She has caused plenty of problems for us and I hate her.
For the last 6 months or so, she has has gone quiet. She is getting married, so hopefully she’ll go away now.
BUT, I work in a beauty salon, and we do stupid parties for groups. She has been with her work twice before. I have just checked the emails and she’s asking about coming again. I don’t when though yet. I feel sick, I just dread her coming here. If it is on a day I work, I will have to take the day off. From now, up until when she comes in, I will dread the phone ringing and the door opening. Last time this happened, I got myself worked up so much, I was ill at work and had to go home.
How would you deal with this?
I am not the type to just shrug it off and think “well I have him now”. I’m a worrier.