I don't think she dresses too old. But I see the Eurotrash vibe, she's just a teenager, it can be just a phase. Or not.
Perhaps not "old" ... I think that given her age and status she could dress a bit more tasteful which would also counteract the Eurotrash vibe.
For the poster who asked what constituted "Eurotrash" ... young people with too much time and too much money who seem to wander from event to event and town to town without much focus or direction on what their lives should be (and, I'm probably being very generous with that definition)