Does anyone know anything about gardening?

Nothing that helpful add except that as someone who has recently viewed an enormous number of front gardens there are three things that will make it look good vs shit over time:

1. Evenness of ground - you can have a slope, but the ground must be even. Lumps and bumps will make it look shit.
   
2. Neatness of edges - unfortunately you've got a rectangle so you've got to to make it as crisp and straight as it can be. But in your favour hopefully you won't have any joins.
   
3. Boarder interface - this needs to be clean and ideally natural (unless you want it to look fun and fake).
   
   
   

Other 2p comments are that I'd pick whether stylistically you want it to look natural or fake.

Also

she wants to be able to use that section of garden year round.

Weedproof membrane and gravel will do that and will take you both about 20mins to put down and give you the option of interspersing plants in the future.