No single witch in a bound circle can perform magic without help from another or a crystal. Jake is now in the circle through Nick's bloodline, yet he can perform independent magic. No one helps him and there's no sight of a crystal in his possession (at least not yet) to explain his ability.
Cassie, waking inside a circle of iron sulfide (which prevents witches using magic), nonetheless performs independent magic under duress, with no explanation other than it's because it's dark magic. Magic is magic, and the preventatives should work whether the magic is light or dark.