How lovely of you!!
My dd is a similar age and so far I've got her (as well as boots and a jacket)
Clinique Black honey gift set (on offer at beauty buys £18 for it with mascara. It's an 'almost lipstick" in that it brings out your natural pigmentation so suitable for anyone. Apparently all the rage on Tik Tok.)
Elizabeth Arden 8 hour skin protectant
Benefit make up and skin care
Tesco Christmas glass with her initial on
Tesco penguin hand warmer
Personalised Heinz ketchup
Her name in Greek lettering necklace from Etsy
Hair towel from L'occitane
Just reading that it's all quite personal! You probably don't want bulky things for her to carry home!
For DS' GF same age I've got perfume (Debenhams has some fab prices), packing cubes (going travelling) and the black honey set.
I think the stocking is a great idea. Can pop in wee bits like cosy socks, a relaxing eye mask, you can buy Tim Tams (Aussie biscuits in some UK supermarkets) Aussie paws paw balm (Superdrug, Amazon etc it's great and generic), some traditional U.K. stocking fillers, some stationery bits.
Is there anything locally made you could get for her that would remind her of this trip when she goes back?
Cosy hat, scarf, gloves as might kit be expecting it to be this cold!!
Pyjamas? She can exchange if she wants.
Some wee home comforts she might not have if she is living out a suitcase - things that could make her life here a bit nicer but she doesn't need to lug home!