I think it depends on your budget and where you live. North America has System76, UK has Starlabs, Germany has Tuxedo, Netherlands has laptopswithlinux and Spain has Slimbook. I think Starlabs are the only ones who do a tablet. Has your wife tried using an external graphics tablet? I don’t use Krita myself but if you want to save money and buy a second hand convertible it might be worth asking/searching on a Krita forum about what others are using from the bigger manufacturers.
I agree. For the spec though, Dell aren’t any better value for money than laptops from the smaller ‘for linux’ sellers. Which is pretty cool. Of course it’s much easier to find used Dell laptops though.