A high-end private school is a world apart in itself, and her friends would be every bit the snooty aristocrats as she is, or the even snootier nouveaux-riches. There's not that much difference between a princess and a duchess, in contemporary royalties.
Social functions without bodyguards would definitely be challenging, especially if they're less than decorous. St Trinian's is fictional, after all.
I imagine that she would have no experience with household maintenance (from operating a washing machine to DIY repairs or cooking), using public transport (and the... colourful people one can meet on the bus or the train, especially late at night or early in the morning), and shopping (she probably never had a budget).