One thing I would add is before she goes have a chat with her about fainting. Some kids have never fainted and don't recognise the warning signs before they do. Standing still for a prolonged period of time in an operating theatre while not doing anything with unfamiliar smells and gory things happening is a perfect recipe for fainting, even in people who are not remotely phased by blood and gore normally. Warn her that feeling hot, sweaty, shaky or any vision disturbance are the only warning signs she might get.
All vets have seen this many times, and she should not feel embarrassed if she has to go out and sit down. They would much much rather she did this than hit the deck and hurt herself. I pride myself on spotting green-tinged WE kids and telling them to sit down immediately or even catching them as they fall. It is inconvenient as I then have to scrub back into my operation! If I was concentrating hard on what I was doing I might not notice they are about to do it. Around 80% of the WE kids I have had observe in theatre have either fainted or had to go out before they did. When I was about 14 I felt weird watching in theatre once myself and made it out of the theatre into the corridor where I woke up a minute later. Strangely this only seems to happen to people once.
Eating a good breakfast in the morning is probably a good idea too, as well as taking in a good packed lunch and a couple of snacks.