Hello! No, we really can't know 100% where it came from, or why her body was so resistant to expel it.
Speculation has been that the toxins were from either spending all of her growing up in a stinky hair salon with chemicals from perms, colours, hairspray, etc or from working in a stinky newspaper/mag press where there was lots of smoking (she had caadmium too) and the ink smells from the presses.