You can still change without it, but without the moon it'll be easier for you to keep control over yourself.

[Derek keeps his voice low and reassuring, they probably should have talked about this before he gave her the bite, but Derek's not great at talking. This makes it easier.]

When you're angry, when you're afraid, when your adrenaline runs high? That's when you'll change, until you learn to control it. The full moon makes the wolf stronger. It agitates your instincts and your hungers, until it can be hard to think. Without it, everything should come easier for you.