I would highly recommend a gap year before uni - it really matures you, and gives you a greater perspective on life.
I took a gap year in 83 and worked as a nanny in the US. This had the advantage of independence from my parents, but still the security of living with a family (who I still exchange Xmas cards with after all this time). I then travelled around the US for a few weeks with a fellow nanny.
I think travelling alone for an 18 year old, in any part of the world, is pretty dodgy. But if you can pair up with someone it's slightly less risky. Plus staying in travellers hostels you're never travelling alone for long.
Good luck, whatever your daughter decides to do - oh to be 18 again!!