To change an old saying its not the size of the Cat in the fight, its the size of the fight in the Cat.
My Princess the Purrfect is My Oldest Cat at 18 , and noone , but noone gets in her path, or near her.
Although she is grudgingly accepting Pouncierge the Precious as a disciple.
I think your Missy will not suffer fools , and will be able to hold her own quite well.