1. Get it in writing.
2. Have the recruiter explain the educational benefits both in-service and post-.
3. Ask the recruiter what duty stations he or she has had and what he or she would have done differently if anything.
4. Find out about guaranteed MOSs (military occupation specialties) or ratings (Navy occupations). Find out about how they go about selecting one for her if she's undecided.
There are personality differences between the services. If she likes bobbing up and down on an air mattress at the enlisted pool between games of golf, try the Air Force. If she likes driving huge, armored vehicles at top speed crushing everything in her way and tearing up the countryside, maybe Army is the way to go. If she likes wandering through exotic foreign ports and getting tattoos that she can't explain later, Navy'll do it. If those tattoos spell out "USMC" and they're done on the forehead with a nailgun, that'd be a Marine... :-)