Go to your bank and order some pounds for her. If they are only going to be there one day, she won't need much--some for lunch and souveniers. If the group is going on a tour as soon as they land, the leaders may not allow the kids time to use the atms. That could be a big time waster, depending on the number of kids traveling, plus they want to get going and keep on schedule.
Pack snacks and gum in a tupperware type container in her checked bag--granola bars, m'n'm's, etc.--as this helps cut down on costs during the trip. She can also use the container to pack small or fragile things or postcards, programs, etc for coming home. Send a water bottle that she can fill and use each day--she might want to put this in her backpack. Also tell her it is okay to say no when people ask for a snack: "No, I only have enough snacks for me to have one each day."
Send clothes that will dry quickly. Send some little travel packets of detergent so that she can do some laundry in the restroom sinks in the dorns if she needs to and dry it in her room. Send some of her older underwear and she can throw it away when she is done.
Keep her checked bag light so that she has room to bring back souveniers. Send a rain poncho or lightweight rain coat and forget the umbrella. I probably wouldn't send a sweatshirt as she can buy one there and have it as a souvenier.
She won't need as much clothes as she thinks she does. Take pants, capris, and shorts that can be worn two days before washing. Take lightweight shirts and wash them. Take one nice dress or skirt/top and wear it for the all the times she needs it--maybe two if they need to dress up a lot. If they need to take their own towels, pack two beach towels.
Avoid jeans as they weigh so much. Keep the number of shoes to a minimum--they are heavy and take up space! Stuff underwear, socks, etc in gallon zip loc bags, take the air out, and shut. Gives you some more room and organization plus they are great to use for dirty clothes coming home.
Forget the travellers checks, the atm card or a credit card for her souveniers and perhaps even her meals is much easier.
Send an extra sd card for the camera. Deleting pictures wastes a lot of the battery life.
Forget the cell phone and get a calling card. Have her use it once at home to make sure it works and she knows how to use it.
Empty out her purse and have her only carry the essentials.
Take some thank you cards. Take a small notebook to keep track of expenses, places she has been, phone numbers and addresses, etc. Take a manilla envelope to throw brochures, programs, flyers, etc into.
You should have an itinerary and a list of what is going on so you know the type of clothes to pack plus any special things that they want brought and items that they definitely do not want them to bring.
Hope she has a great time!