All the 7 y olds I know are still happy to play with toys too!
For girls of that age you can't normally go wrong with craft stuff and stationery. If you have a Flying Tiger nearby head there and max out on inexpensive sequinned notebooks, colouring pencils, pens, glittery stuff, stickers, sticky notes, paper stuff and crafty things. My nearly 7 yo DD would love nothing more than a box of sellotape, glitter glues, coloured cards, ribbons, and crafty items, and they'll all get used in some way.
If your niece is creative, you can't really go wrong with a watercolour paper pad and some of those colouring pencils in a tin what you can use a brush on to make into watercolour paints.
Galt craft sets are good for that age, too, and decent quality. Galt also do a range of very good and reasonably priced science sets, eg. Science Lab, Rainbow Lab, Magnetic Lab, for about £12-13. My DD loved the Rainbow Lab.
Nightlights, battery fairy lights, bouncy balls that light up, any stuff that lights up to be honest: they love it all. Rex London does cute nightlights plus lots of super-cute unusual toys and stocking filler type things.
The Book People is great for good value inexpensive book sets for that age group. Enid Blyton, Darcey Bussell, Worst Witch etc. all very good.
That age group still loves soft toys and is also normally keen on a bit of tat
so a beanie boo toy or something like a Twisty Petz thing often goes down well. (I am keen on Twisty Petz for presents for girls that age because they satisfy the small girl urge for glittery tat but they are also Small and Easily Tidied Away so other parents like them too
)
My DD is getting for Christmas from us:
Lego
Narwhal beanie boo
Unicorn colouring cards/pad
Metallic colouring pencils set
Some book sets
a Twisty Petz bracelet
wooden cloud bookends
cloud nightlight
Aquabeads keyring set
Nail art set
Pocket microscope.