If this was my daughter I would:
A) Take her shopping beforehand and make sure she has all basics she needs (take her to Savers and get her san pro, sun screen, after sun, deodorant, toothpaste, condoms (if there is any possibility she is or might become sexually active), insect repellent, plasters, paracetamol etc - not necessarily in the luxury brands she might want, but to make sure she has the basics she needs to stay safe, clean and healthy.
B) same with clothes - I would talk to her about what she is planning to take and buy her basics from Primark if she is short of anything she might need (bikini, sunshades, enough pairs of knickers....)
C) if it's self catering I'd buy her a load of noodles! My friends and I lived on these when we went on holidays at that age - it saves you a small fortune.
D) buy her travel insurance myself
E) offer her the choice to have additional spending money as her early birthday and Christmas present. (I'd stick to this too - she would only get a few small gifts for birthday/Christmas if she went for these options.)
F) Ask family members if they will do the same - any uncles or aunts, grandparents who would give her the money they would otherwise spend on stuff for her birthday)Christmas might be happy to give it now instead?
My goal would be to ensure my daughter had a great time, and learnt more about budgeting and living independently (which it sounds like she needs) while also being safe. If she fucks up with her money and spends it all in the first few days and can't go out partying for the last few, that's a lesson - but I wouldn't want her to be without sunscreen or basic food to eat in an attempt to economise!
Hopefully she will do well and have a great time! These experiences are so formative.....