I think you need to understand the usage of the headphones before you can start narrowing down what is required. The primary use case seems to be with a tablet, so I'm going to assume that some form of bluetooth headphone is required, if Mrs 7 is happy to use a dongle though that opens up wired headphones as an option - much cheaper and greater choice overall.
You said she wants neither in-ear or big boxy headphones, but you haven't stated whether you want on-ear or over-ear headphones, this makes a drastic difference to comfort over longer periods. One reason why "big boxy" headphones are popular is that for extended periods they are incredibly comfortable, Mrs C tried using a bunch of headphones which were all small and "cute" enough for her, but it wasn't until she tried some of mine that she changed her mind about them, I gave her my set of Bose 700s which she finds very comfortable for use over long periods.
There are a lot of smaller headphones which you can get which might work, but frankly I would avoid, without spending quite a bit of money you will end up with terrible sound quality and poor construction. I would try to stick to a good quality headphone brand if buying blind (Sony, Sennheiser, JBL maybe).
Headphones are generally quite a personal choice, when I first started to listen via headphones I used to be able to go into a shop and listen to a few pairs to see how they felt on my head or sounded. Sadly they started to disappear in the 90s, the last good one I remember was City Radio in Liverpool.
FWIW I'm down to 7 pairs of headphones now, but that may change in the near future, they're easier to hide from Mrs C than bikes