Probably not clothes as I've done that for the last few birthdays/xmases, and I'd really like to come up with something different. Not tech - she's got a phone, and have agreed with ex-H that we'll jointly get her a new laptop for her 16th birthday ready for 6th form.
I can do small presents/stockingfillers easily (posters/books/stationary/earrings etc always go down well), but am struggling for a main present. Budget probably around £50 but could spend more for something perfect IYKWIM.
She's into fandom stuff (Vlog brothers / Harry Potter / Steven Universe / endless tumblr blogs), space exploration, general geeky sorts of things.