I think Lola Rose would be nice. They don't cost a fortune but are not cheap / tacky. You could get her a necklace in something classic - white / black / grey, or maybe opt for pink / purple or - a turquoisey colour - which is "bang on-trend" this season. This summer it's all about aquamarine and blue turquoise, so anything in that colour spectrum would be nice. Kipling bags, again are not too expensive and come with a fun monkey attached. I'd probably buy her a stretch bracelet. Whatever you do, don't buy her a Michele Hope stretchy lace cardigan in dusky pink!
I would say find out what colours she likes and buy her LR. I'm not a girl but I remember when I was 16 I wanted to look older! Now I want to look younger! I think if you choose the right LR piece she will really love it. Although I don't like the LR guest and her silly voice, her jewellery range does transcend all age groups. When you buy for her, think of buying for someone who is 21-22, as that will likely be what she is aspiring to.
This comes in different colours:
Or the black and white is a safe choice:
This is really nice:
This friendship bracelet comes in different colour options and is nice:
Oh, Julius, you have taken so much effort looking up, I am ever so grateful , thank you so much