I don't think it's a difficult age to buy for you could have got her
Nice new Pj's
Slipper socks or funny slippers
Make-up
Headphones
Books
A magazine subscription
Some nice perfume
Stuff for her nails
Stuff for a hobby
Some nice bits for her room
A new bag/purse or backpack
You can buy gift cards for cinema's,coffee shops,dessert places,milkshake bars,multi gift cards(that you can use in lots of different shops)gift cards that you can use online for games or music,gift cards for hairdresssers/beautician's/nail bars.
A camera
A tablet
A new phone
A nice piece of jewellery
A pair of trainers/shoes or boots she had chosen.
Some bath bombs and face masks.
There is so much choice out there now,we have 5DC,3 DS's and 2DD's and so far I've managed to get them different bits every year,I usually do a few bits that they need,some things they can wear,some things they can eat,some things they can drink(the food and drink thinks are usually unusual or expensive)some things they can use and they usually get at least one piece of equipment each year,weather it's a games console,a phone,headphones,tablet,laptop,camera,a musical instrument ect.
With my oldest DC I just usually listen to what they talk to me about,new music,clothes,electronic thing that they're into and I check out what they're sharing on social media now and again(they all have me on they're accounts I'm not being sneaky)and I ask the other DC if there's anything each other as mentioned that they think they're brother or sister would like.
I think like PP's have suggested set up a nice day out for just the two of you but don't sell it as an after thought tell her it's one of her Christmas presents,I would have loved that at her age and I know it's something all 5 of our DC love a bit of time on they're own with mum or dad.