Yes; she ends up being one of the two most heroic characters, in a cast full of them. One of my complaints with the Harry Potter books was that the people seeking to remove obstacles from Harry end up being far more heroic than he is himself. That's not the case in this series - there are plenty of people who set out to help Lyra and do it heroically, but she rises to the challenge and is a hero in her own right.

The alethiometer is explained more thoroughly later in the first book, I think, but it's used extensively in all three.