What to do about drugs? Serious answers only please.?

If she's your friend, just talk to her. If it looks like she's overusing, there may be a reason for it. Quite frankly, if you only smoked twice and haven't since then, don't be to afraid of your parents finding out: if she tells your parents, she'll only be admitting what she did. And quite frankly, I find it unlikely that her parents haven't noticed she's smoking, unless they aren't very involved with her (which might be part of the problem).