Am I over reacting?

My fiancé and I have a mutual friend. Let's call her Jane. I was close friends with her first, and then they started working together. He is her boss. She's always trying to join us on road trips and every time he visits my work, she'll suddenly be there as well. She tried making fun of me while I was working because I was cleaning counters and apparently in their restaurant, cleaning stuff isn't suppose to be anywhere near food. I work literally in an ice cream parlor. There were sweets everywhere. Well, she's always trying to get him to hang out with her and she's always incredibly flirtatious stealing his phone and taking selfies on it. She started telling him that she saw her boyfriend more as a best friend and that she likes someone else. He kinda cut himself off and now he's trying to maintain a professional relationship with her, but she won't stop trying. Am I wrong to be upset towards her? Or to the situation? Please leave feedback.