Just remember that she's 21 and will probably be going out with other 21 year olds (or older guys who might be immature it socially challenged if they're seeking out dates with someone significantly younger than themselves). She is much more likely to encounter douchey pressure to drink more than she wants than someone in there late 20s. 21 year olds are just a bit more naive when it comes to social drinking situations.

I'm not saying she should do anything differently than what you suggest, except that she should be more mentally prepared for rejecting pressure to drink because a lot of guys at that age don't know any better. When she encounters such a guy and rejects his pressure to drink, hopefully he will realize social drinking situations don't all have to revolve around pressuring one another to drink more.