I also have 2 DDs, and a DS. My cardinal rule every Christmas is that they get roughly the same amount spent on them (one memorable year I got both girls' presents to within 50p of each other, yes, I am that scrupulous about being fair!). They also have to have the same number of presents to unwrap.
I look for gifts that have the 'wow' factor, so I listen carefully to what they admire over the course of the year and then I buy it. I was lucky this year to have a trip to NYC and I bought a lot of bits there. They are 21 and 19, and I do buy them clothes sometimes. I have a pretty good idea of each one's (different) style. Spend time with them, go window shopping, listen to what they admire that their friends have etc. And yes, of course they wear jumpers, and so do their friends!!
DS was a little amused (he's 15) at the three body wash sets, but as I explained, they were 3 for 2 in Boots lol! He also got hoodies, T-shirts, books and what he's wanted forever, a goddamn Nintendo Switch plus games.
Does she like jewellery or makeup? Nail varnish? Read books? Like concerts or music? Have any hobbies? There's so much you can get a 16 year old, I think it's a far easier age to cater for than 10! You just need to put some thought into it. For example, DD2 got the Greatest Showman piano book for her birthday - she has grade 8 piano and she saw the movie 5 times, lol. DD1 adores our cat and loves jewellery (DD2 adores the cat but doesn't wear jewellery much) - so she got a lovely silver necklace with a cat washing its face. I bet there's lots you could think of it you just use your creativity and join a few dots!