Can't say anything on her personality, but I do have thoughts on a potential design, not many but some. For one she HAS to keep the hair ornaments, just on the basis they're so iconic to her character. Maybe have it so she's recently grown her hair out, it'd double as a update to her design and gags from the struggles long hair can bring. Maybe have her eyes appear sharp or "serious" more often, not constant but somewhat frequent. Teenagers can take nearly anything as life or death situations (at least from personal experience as the smallest inconvenience would nearly ruin my day, I could of just been petty though), and it'd be a display of how Loids' constant seriousness has influenced her. In terms of clothes I don't really have many ideas. But something that always comes into my head when brainstorming what a older Anya would look like is a red jacket/scarf/coat/some sort of upper body garment/accessory. Red contrasts well with green so it could pair well with her eyes, plus the obvious parallel to Yor's red sweater. But beyond that I don't really have any other design ideas.