You can often get a deal on a Festival bundle of camping gear that comes with a tent, foam roll mat, & sleeping bag if you look online or in camping shops. I agree with suggestion for dd to put it up at home beforehand so she knows how it goes together and how to pack it away. How many friends are going? Get a 2 or 3 or 4 person tent as needed. It would be good to find out what camping gear the friends have, too, so you don't buy more than you need, and some things can be shared by the group.
You should decide whether to mess with a camping stove. They can be fiddly and dangerous if you don't know what you're doing. You should be able to buy hot choc/coffee/tea/breakfast roll from a food cart, if you need something hot.
I never bother with the showers, just tie back hair, use wet wipes and/or wash cloth, change clothes.
Expect queues, have patience!
Bring clothes for sun & rain, chilly nights
(Colourful, costume-y, fun!)
Wet wipes, Loo roll
Snacks
Water
other soft drinks, no glass, be prepared to carry them!
Flashlight (head torch is super handy or a small one that clips onto your backpack)
ID, small amount of cash, card
Phone, charger, power bank
Sun cream
Toothbrush/paste
Wash cloth, small towel
Plastic bags
Picnic blanket (with plastic side and fabric side)
Comfy walking shoes
Wellies if rain expected (bring lots of socks)
Sandals or flip flops for around the tent