HELP - how much money for a teenager?

Hope someone who's visited this year can help please?
we're taking our daughter's friend with us for 18 days in August and her mum wants to know how much spending money she'll need - to cover all food and drink as we are SC
14 year old so will be drinking soft drinks, eating out every evening and probably lunch too, will also be doing boat trips so what's the going rate for them this year?
am trying to come up with a daily allowance and some money left for getting bits and pieces from the markets
we're taking our daughter's friend with us for 18 days in August and her mum wants to know how much spending money she'll need - to cover all food and drink as we are SC
14 year old so will be drinking soft drinks, eating out every evening and probably lunch too, will also be doing boat trips so what's the going rate for them this year?
am trying to come up with a daily allowance and some money left for getting bits and pieces from the markets