I always wondered that as well, maybe mito was the queen XD jk but it's sad she doesn't even possess a imperfect version. Unless it had some super healing ability along with it i don't see why she would have used it against Madara since he wouldve been able to take her out easier.
We can just settle on her getting that nickname just because her trademark summon is the slug and probably somethign known by alot of people