The engraving idea is a good one, and I’d take the same approach with something she can keep even as her style changes. A necklace, bracelet, or ring can carry that little bit of meaning without turning the gift into some giant ceremonial thing she’ll never wear. You can look at some jewelry, for example, here: https://pierrejewellery.com/ . There are enough different styles there to find something that feels like her rather than just choosing a generic birthday piece. I’d pay more attention to what she already wears day to day and pick from that direction.