I'm disturbed and confused for my friend....please help?

My guy friend has a boss who is about 15 years older than him. She's very flirty with him....she makes a lot of eye contact, she smiles at him in a seductive way, she asks to work with him, and she'll find subtle ways to get physical with him without it being out of line. The thing is, she's in a relationship....but when her significant other is around, her personality changes completely. I think she's interested in my friend but I need some other opinions please....could it just be the way she is and he's looking into her signals too much? Thanks!