imo, you should just have the tile removed; it is totally unnecessary. Any mirror is going to be too high above it - and I don’t think a mirror can be secured well on top of the tile. And imo it also doesn’t add anything to the design. Someone else here may differ and/or have an idea for you to affix a mirror over the tile. I would just remove it. It does not work. A kid’s bathroom mirror has to be very low, if they are going to be able to see themselves in it, or it’s pointless. I’m sorry this happened - and I understand the inconvenience. But mistakes happen.

Pivot mirrors? Let the bottom edge be over the tile...

Take the tile off. It was never needed anyway. Smooth out the drywall behind it. Have the contractor make you a frame, right on the wall and ALL four sides, the whole vanity space , edge to edge and top to bottom using 1 x 2. Paint it to match vanity. Call a glass company and they will template, and cut a mirror to fit inside it EXACTLY. They will glue the darn thing , one mirror for the entire vanity space. Sturdy? You bet? See yourself from anywhere. Unmatched wall textures? Gone.

Somewhere everyone got the idea that you HAD to have a free hanging mirror or be very un cool.

Answer? Dead wrong. Mirror the entire space and move on: ) Return the mirror/s you bought or use elsewhere.

Want the extra cool way? Go to the ceiling with the frame and mirror, and THEN mount the light, right ON the mirror. The glass company will account for the mount, the hole for the electric will be in the mirror for install.

The whole thing should not set you back more than a few hundred bucks, because thankfully, mirror is cheap. The matched frame will look great. When you buy a free hanging mirror? You are mostly paying for frame : ) not the glass.

Easy..... Blue frame? Fine in white too

Your counter has a built-in backsplash. The extra tile on top is unnecessary. Remove.

You didn't say the size of mirror, but if it doesn't take up the whole area of the non-textured portion of wall your remodel will look rather undone. You can match/overspray the old with texture to blend in well enough. Or a little more work since it's painted, smooth it over.

Actually, forget what I just said, zooming in I see the vertical corners and right above the tile are cake frosting and it looks like there was a wallpaper frieze or former fix at the ceiling transition, so the texture is really just a band even with the light. So smoothing this wall appears the way to go, and will match the level of your new vanity. Then combined with removing the tile you can have any size or style of mirror(s).