What a wonderful opportunity for you! Having been through natural labor and delivery 3 times, I would say that the most important thing you can do for her is to LISTEN. Every woman needs something different when they're in the midst of such pain and emotion, and each experience is different. Know her birth plan and what she thinks she'll want and need beforehand, but that could all change in a nanosecond so really pay attention during the process. Some women want to be touched and massaged, and I always thought I'd want that, but then in the moment I did NOT want anyone touching me for anything. Just be there for her and be at her beck and call for this amazing experience.
As far as tricks, I only know a few... tennis balls to massage her back, a sock filled with rice that you can heat up in a microwave to apply heat to back and neck (not sure how you could do this in a hospital, but for laboring at home it could be great), I've heard that to smell a lemon (freshly sliced) can help any nausea...
Good luck!