First time you get caught is always really harsh on them. They picture you as their perfect little kid and when they realise you are using drugs it breaks that mental picture. Just let her calm down, after a couple of days or even a week. Tell her why you were using weed and how its helpful not hurtful. If she changes her opinion on it, yaaaay. If not you have to choose between being able to smoke or having no trust with your parents.