I believe for seasonal employment, you only have to work a couple of shifts a year, but that can vary from department to department, but the requirements are few.
If you are under 18, you can work foods (the carts, no usage of large machinery like big mixers and slicers), merchandise, games, and park services.
I wasn't aware that attractions drug tested, and if your friend is concerned, I suggest she not do drugs. Most large corporations do so these days, even for low-paying jobs. To ask for another department might look suspicious. I would say she should take her chances.
Since everyone wants to work a brand-new attraction, and most open positions anywhere are posted internally first, current team members do get hired first.