If you think it really is a way to goad your son, I would isolate the child doing the taunting. I used to tell my son, “find your joy somewhere else.” He would seem to delight in agitating others.
If your daughter really needs space from your son, I would take that seriously as well. Sometimes my kids will request “alone” time. they just need to have space. As someone who needs space myself I tend to sympathize with this.
Really I think it is important to see if you can discover the root cause of the behavior. Perhaps she is just discovering a new way to exert her authority over others. Or maybe a sensory issue. The solution could look different depending on that cause.