Hey, For 12 year-old, you can buy; clothes, books. She is about to enter teens and it is quite a confusing time for kids this age, so you can gift her book on how teens are like and teens related issues and their solutions. I mean you can search the bookstore and can opt for the apt book. You can also gift Kindle, so that she can read as much. You can also gift DVDs of her favourite movie, or any inspirational movie. You can take help from the shopkeeper as well in selecting the movie. You can go through the link below and decide what to buy. https://www.thepresentfinder.co.uk/dept/teenage-girls-presents-gift-ideas_d01172.htm
12 year old are at a age of proceeding to secondary school. Stationery or Accessories would be great. Since CNY is round the corner, probably some clothes? Best way if to get vouchers! she can be a little adult to decide what she really wants and be happy with her own purchase
How about a bag? Something like a satchel bag or anello bag (http://www.bagstore.com.sg/). You can also consider maybe stationery from smiggle (http://www.smiggle.com.au/shop/en/smiggle/stores/sg) or planners/organiser from Paper stone http://www.thepaperstone.com/