However, Exio wont ever be fooled by Arya's face changes; his Eagle Vision, which gives him the ability to differentiate between friend and foe, will immediately see right through her skin masks.
Along with this,
Now, let's look at the 800 pound silverback in the room; gender
Plus, in martial arts, people learn to use their flexibility, balance, and as many muscle groups as possible when doing a technique, thus giving a smaller person the potential to strike even harder than someone who is larger and strong than they are.
Along with this, he also has firearms, weapons that, to my knowledge, do not exist in Westeros (though guns were known about in the latter dark ages, I've never heard of hand cannons (early guns) appearing in GOT).
Thus, Ezio has a tech
If this was the Arya from the book...then its possible that in a face to face encounter, she'd get the drop. His eagle vision would clash with the fact that a small girl was standing before him, and if he hesitated (quite possible. This is a child, after all), then
However, this isn't the Arya from the GOT books; this is Arya from the HBO series, who isn't daddy's little girl anymore.
Though I think Arya has what it takes to sneak up and take Ezio down from behind, when it comes to a clash, most
(pun intended, in more ways than one!).