If it must be a surprise, then you can’t go wrong with a Fender P bass. I must have gone through around 15 basses in my first 10 years playing. I tried loads but the one that stuck was a £350 P bass I got for my 16th birthday. Maybe find one in a colour that is a bit different or fits her tastes? Or if you think a smaller scale could suit better then there is also the mustang range.