Tickets to a music event as a surprise.
Take her to someplace she can dress up – meal, theatre
Day trip or weekend to some city (maybe include voucher for her favorite fashion or music shop?).
Take a look though the web sites for those 'special event / red letter days' for ideas.
Listen to what she mentions a lot and buy something related to it or something she has pointed out as 'nice'. Lots of people inadvertently give 'gift clues' all year round. Try to remember them as they are useful bits of info to have!
Take her on a road based bike ride as many people find that less intimidating than off road – maybe bike to a birthday treat or event.
Jewellery is always good and has a big price range.
All I can think of right now.