It's controlling plain and simple. She invited herself and is intruding on YOUR time with him. I would SERIOUSLY uninvite her or ask your BIL to change the plans where she isn't going to be able to make it.
Just the plain fact that he's your BIL and not hers makes it all suspect. She wants something plain and simple.
How did she even know he was coming?
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.
