My DH does triathlon, and our son did 1 so far. Many kids don't have specialized equipment. A lot of kids just use their regular mountain or hybrid bike. But, if your daughter has or can borrow a road bike, she might be better off. (If the bike course is on a paved surface. If it's off road, obviously ignore that suggestion!) If you do borrow a road bike, make sure the pedals don't require clip-in shoes. If they do, ask if the owner has regular pedals she can use, as using clips takes a certain amount of practice to get used to.
Where will the swim take place? Is the water warm enough for swimming? If so, all she'll need is a suit that won't slip off (most girls seemed to wear one piece suits). If it's cold, she might want a wet suit, but I would look around to borrow one. She should practice getting in and out of it as well as swimming in it before her race.
Let me know if you need more info! I'll try my best to help. Good luck to your daughter!!