The fireplace is not so bad. The floors and the mismatched shelves and mantle are what doesn’t work.

I’d remove all shelving and mantle. Build a bar on the left side with slab cabinets. Unify colors. Perhaps you change the flooring perhaps you stain the brick.

Don’t fight the MCM. Decorate the room accordingly. But, if she hates MCM, post pics of the rest of the room so we can see her style.

I would start by removing all the shelves and decor.

what size refrigerator are you hoping for? Fill in the recesses with cabinets to match the existing sink cabinet and paint the cabinets to compliment the existing brick.

The fireplace looks fine. Add a mini fridge and small microwave for popcorn and nachos on the right side.

She could replace the shelves with artwork or mirrors, but the shelves are not offensive. They are probably going to be useful.

Agrre with above suggestions. I would also have a new mantel in the same or complimentary wood and style of cabinets and shelves. Shelves on right should be lowered after installing another cabinet, microwave, etc. The cabinet could hold snack supplies, shelves hold bowls and plates for snacks.

I would remove the mantle. Get a thicker straight piece and wrap it into the alcoves on each side. Remove the shelves on each side and do thicker shelves that match the mantle. Change out the cabinet for a navy or charcoal color with a top that is similar to a color in the brick.

The floor is busy, the brick is busy, the shelves and the red countertop create movement for the eye too. Each piece alone is fine, together they are a lot. Most fireplaces of the split level era (including mine) are asymmetrical. the part to the right was for storing the firewood.

IMO, the white cabinet tones it down. I"d remove the shelves or paint them a color that blends with the brick and cover the floor. Light wood console instead of the dark. Again, too much contrast. Tone it down.

I would take down the mantle to make it more MCM

I would change the shelves to a thicker dimension and make them 'floating' without the brackets. See below for shelving style. Add a fridge.

Bev had about the same suggestions as I was thinking with just a couple of minor changes.

Fridge has to be on the non sink side. I might match the fridge and the cabinets - all black stainless or stainless, or a color - would not do white - stands out more than I would want.

(The front of the fridge can be wrapped with 3m wrap like they use for cars, so you can broaden your choices without breaking the budget.)

You can get under counter fridges with a small ice maker, can get them in different widths, can get them panel ready . . .

This site has hundreds of them

https://www.pcrichard.com/undercounter-refrigerators/?prefn1=ecp-refrigerator-width-%28in.%29&prefv1=15

on the other side I would add a large floor vase or a set of 3 or possibly a large sculpture

or shop till you find something incredibly unique for the space like this 24" tall Giraffe lamp.