Have you thought about stainless steel backsplash tiles? https://www.houzz.com/products/4x11-honeycomb-matted-metal-peel-and-stick-backsplash-tile-set-of-3-brushed-st-prvw-vr~100903589. These tiles would look great with your stainless steel appliances.

I don't know what your client has in mind completely. It might be worth asking the client for some inspiration pictures for what she has in mind. I think some glass mosaics might be overpowering for that granite. But there are some glass mosaics that might work as long as they are very plain. Super white glass tile Maybe something like this with a tiny bit of pattern: Silver planks glass tile Or maybe this one which might work with the colour in the counter: glass mosaic - raw silk

OH BOY. I'm sorry I know you must be unraveled, but realistically it looks more like the counters dont go with your kitchen as they are brown tones and everything else looks black white and gray. Why did you leave the granite backsplash up? that would help minimize it a bit I think.. We need to see the whole room.

Agreeing with others, but want to add. Not only is backsplash choice last, but it also should not be chosen until after everything else is installed. Everything looks entirely different after it is installed, and if you choose your backsplash before that, you will make a mistake. Don't worry about not having your GC still available for the backsplash after everything else is installed. You will actually get a better backsplash installation if you hire a tile installer yourself. Remove the backsplash from the GC's scope of work, and hire someone yourself later to install it.