Well, yes, although it is hardly Rider's fault that she is like she is.
Does not matter really. Not the fault of magi that they where born that way either, but they still Heritics. The church hunts heritcs and inhuman monsters, it is just what they do. If they are born that way means nothing to them.
Except that said kid would be trying to kill him, because, to him, Rider is not a "monster", Rider is family. If you kill his aunt (or even attempt to do so), then as far as he is concerned you are a monster yourself, and nothing you say is going to convince him otherwise (at least if successful, if you fail it's possible that an apology and a promise to not do it again would be enough).
He think it some sort of mental control, he has seen such things, both by dead apostles and by the vampires of the city (especially since some of the kids he takes care of where basically being treated as mobile blood bags). He would basically treat him as a kid with a lot of trauma and try to break him out of it. Not that that actually what it is.
And, no, he can't be "disarmed" (because he uses magic), and nor is the fact that he's horribly outclassed going to stop him (because he's a kid, and his parents keep him the hell away from anything that can endanger him).
He will be bound by his shadow the moment he takes a hostile action to Shiro, a very effective method of stopping brainwashed kids from going bonkers. Cause he can do everything Ciel can do with Black Keys but better.
Killing Rider wouldn't be easy, though, she is still a Heroic Spirit.
No she is a servant, very diffrent. And Shiro can fight servants. Ciel the weakest can only fight defensively vs them, number 4 can actually match them. He is a
monster.
