i'd see if you could remove the 4" backsplash first. yes you can add a row of mosaic but it will look like an add on. better than a damaged wall, but still not as good as the mosaic going down to the counter top itself.

You can add a decorative row of mosaic just make sure the thickness is the same and then add a liner to finish it off.

no. it would look like you're trying to cover up something. can you get a larger backsplash piece? maybe a 6"? why wasn't that addressed when they were installing it? if not, remove the 4 inch piece and pick a tile to backsplash up the wall to under the mirror.

I thought it was and then they installed and it's shorter than the side splash. I think ordering a new one is the best option. I'd like to tile it all but then that's just one more project I have to take on. Thanks.

the side splash should be equal w/the front. how in the heck is it shorter?? sounds like it's on them.

They are the same height. I think they just damaged the wall when they removed the old granite side splash. I'm going to call them and either have them remake them or remove and go with tile. It's about an inch and half of dry wall damage all along the new side splash.