Book for that one older aunt who’s read every mystery novel ever written.

Looking for a birthday present for my 70F aunt who asked only for "a good fiction book." I read a ton through my library, but almost exclusively fantasy, some of which leans very YA. So, I have very few personal recommendations to go off of.

One series I'm considering is the Thursday Murder Club (I've read the first 3), but I'm not sure if it's a little too twee in tone? She's leant me one book from her Robert van Gulik collection, but I haven't gotten around to reading it yet :/ I know she's always had an interest in Chinese & Japanese culture as well, so any novel with those settings may work, too. I'm just guessing that she's probably read or sampled every mystery series that's over 10-20 years old, so I need ideas for other books she may not have gotten to yet! Thank you 🙂