In my opinion, your open to MANY, MANY, MANY problems here.
Adults CAN'T keep secrets, much less children. Lets say;
1) A 14 year old is caught with weed by his/her dad, which is also a cop, the kid (stoned as hell and scared), says "my friends brother", even if you had nothing to do with it, game over.
2) A couple teenage boys, high on other drugs and alcohol and pot, want to impress their friends and girlfriends or are just looking for a free ride, come to YOUR house.
Those are just the 2 most likely. Remember the #1 rule for growing,
KNOW ONE KNOWS !
Maybe you should keep clean til a month or so after she leaves.