Law attacked her, but nothing happened.
Zoro could have at least tried to damage her like he did with Kaido. He never even attempted to do it.
Same thing with Killer and Kid.
Luffy wants to fight Kaido, so he doesn't seem to care about BM.
There must be a reason for why she has never been...
Absolutely. She could actually save herself imo and it would be really anticlimactic for her to just drop down like that. Her hair is still burning so she could use that to save herself too. We just have to see what she will do.