I would make the mirror the width of the wall, I'd do the same with the vanity, custom build one to match the wall dimensions. I also change the light to something more simple and flat. I'd work to make all the same color, meaning no dark wood trim or anything. Create a solid flow of material.

If it were my powder room, I think I'd keep a pedestal sink, get 3 matching rectangular mirrors, spread them across the 3 walls, and mount them lower than shown (so that there is a bit of wall space between the top of the mirror and the bottom of the light bulbs, assuming you want to keep the fixture).

I have a strong aversion to downward facing light fixtures -- I dislike seeing bulbs lol -- so I'd change the fixture or flip it upside down.

I'd also paint the walls a happy or dramatic color. :-D

As an alternative, we replaced a pedestal basin with this small vanity in order to have some storage. Then installed pendant lights adjacent to a narrow mirror.

I would keep the sink and change the mirror to something the same width or wider if you can find it, and longer. I know that is not easy to find. I needed a powder room mirror no more than 18" wide and had a very difficult time finding one that worked. I found a mirror meant to hang on the back of a door just in case you are having a hard time with the size.

Not often considered, but an easy and cheap way to upgrade your bathroom is the inclusion of light fixtures. Even installing a small sconce near your mirror can greatly change the mood and lighting in your space.

How about finding a 3-panel vanity wall mirror that would fit in the space? It would give you a wider mirror surface and fill in the weird angled walls.

Chispa beat me to it. A 3 panel vanity mirror...or put a larger mirror edge to edge on the flat wall, and then put sconces on either side on the angled walls.

I 'like' Beverly's, and a simple shape for faucet // 5.5" H x 16" W / steel and etched opal glass shades with integrated 9 watt LED lighting capable of being dimmed. Energy star certified. Mounts to either a 4" square or octagonal recessed electrical outlet box. Mounting strap for outlet box included.

Progress Lighting P300064-30 Volo 2 Light 16"W Integrated LED - Brushed Nickel · More Info

with good reviews -

Luxier Lead-Free Bathroom Sink Faucet, Chrome · More Info

Maybe?

water runs through the frosted glass creating a 3" wide miniature waterfall. Specifically designed to accommodate a vessel sink, this single hole faucet is designed to be mounted directly on the counter. The taller faucet design provides more room under the spout for washing and cleaning those hands.

Squared Waterfall Vessel Faucet With Clear Glass, Chrome · More Info

Waterfall Faucet Cast Satin Nickel 7" H Glass Short | · More Info

I like them, so new! ... but $126.

for recessed and above counter sinks. Solid brass construction with a tarnish resistant, Satin Nickel finish. Top rated high quality internal cartridge tested to last 500,000 cycles. Features a modern solid brass joystick style handle. Comes complete with supply lines and mounting hardware. Purchase additional round glass disks to change your faucet look! Overall height is 7 inches.

good reviews, for 274.

Also in nice blue, and white.

18" Gray Sink Vanity · More Info

cabinet inlay, pillar detailing, integrated sink top, spacious cabinet, for transitional, contemporary and traditional designs. Does not include faucet or mirror. Materials: MDF/veneer

Also walnut color, and white. W 20" / D 18" / H 33"

Urbania Vanity Set, Gray, 20", Single Sink · More Info

constructed of durable plywood material. White Matte finished in melamine, and contrasts with black frame for stark effect, Walnut color, dynamic with a visible grain. Dark Gray with melamine finish, the wood grain showing.

I'll delete what you don't click a 'like' for --

LED Waterfall Glass Spout Single Hole Single Handle Bathroom Vessel Sink Faucet · More Info

• The LED light is powered by water flow and will change color with changes in water temperature.
• Constructed from solid brass.
• Features a waterfall spout design that delivers a gentle cascade.
• Vessel faucet for above counter sinks.

If you are having trouble finding a mirror the exact size you want, you can go to a local glass shop and have them cut you a mirror the size you want. Then take it to a frame shop and get a narrow frame put on it. You will have a wide choice of colors and materials for the frame.

How about finding a 3-panel vanity wall mirror that would fit in the space?

:-D

This is exactly what I envisioned when I posted, lol! I just couldn't think of another way to say it, other than "three mirrors spread across the walls." Yay sleep deprivation. ;-)

Below are a few powder room designs of ours. Maybe looking at them will help you make a decision on what you want to do to redo the space.

Evergreen Renovation: Powder Room · More Info

Golden Renovation: Powder Room · More Info

Cherry Hills Residence: Powder Room · More Info