Sure she can. She can leave for Armonia where they do have Cavalry! 
Cavaliers are meant to be the most honourable people around. From the wiki: ''A noble fighter, a knight of the realm. Cavaliers are highly respected knights who subscribe even more to the life of a nobleman."' A knight of the realm. And as such they can command more cavalry but they are not a class just about commanding cavalry.
So in Siana's eyes jumping ship for gold doesn't seem like a very honourable thing to do. But then she doesn't think many Armonian's are particularly honourable
PS Indirik your centre is still pants
But it's true we do have 2 Cav centres now.
