If you want to spend more on some items you could wrap up little comments about you and her as mini presents.
Her favourite chocolate bar, a pretty mug with something she likes on it or personalised, a photo of the two of you in a frame (you can do all sorts to them in Boots and other digital places), a friendship card (from most christian bookshops and some card shops), a CD of her favourite songs you could make for her, a list of the 18 best memories of you and her, you can get some lovely keychains or phone chains and accessories from H&M and Primark, a fancy scarf, a mini silver compact mirror, lush do some gorgeous bathbombs with dried flowers in, if you go to counters like Clarins or Clinique they sometimes have mini treats they give out.