Remember all a cop needs is probable cause to search a vehicle.
That's a big 10-negative, good buddy.
A search can be made incident to arrest, and can include ONLY the "lunge" area (where the driver can reach), and can not include locked containers, a locked glove compartment, or the trunk without a warrant or without the owner's permission.
I agree with one of the other posters when they said that the officer had no way of knowing if the smoker was 18 or not. If that is all the officer can articulate, there is something VERY wrong here.
I would get from your daughter the following information:
1. The name of the officer conducting the stop; if not available,
2. The time the stop was conducted,
3. The location of the stop, and
4. The police department conducting the stop.
I would then call the department's commander of patrol or the chief, and ask to have made very clear EXACTLY what articulable offense the officer witnessed to make the traffic stop. Do not accept any run-arounds, hemming and hawing, or vague answers.
It sounds to me like the officer was engaging in some questionable activity, and has no business in a patrol car. Period.