The kitchen photo uploaded, the bathroom photo did not.

If this is used as a pied a terre for only a few days per month, the kitchen has far more stuff than would be provided by a luxury pied a terre rented from Airbnb. Look at some of the Airbnb apartments online to see what the differences are. Then you can help your friend pull everything out of the kitchen and reduce the amount by at least 50%. Look at the decorative objects (framed prints, other art, knick knacks, rug, etc.) and decide if they look more than a bit worn or suitably antique, depending on what your friend really wants now.

The photo looks like the green wall paint and gray ceiling are a bit gloomy. Is that the case in real life? Try changing out the light bulb to a brighter LED in "bright white" color temperature. I assume you have to leave the fixture itself alone since it is part of the apartment.

The tile floor can be professionally cleaned and then the dark grout can be painted the same color as the clean tiles. It will look new and fresh.

Is your friend allowed to paint the walls or replace the appliances?

Looks like more storage is needed. I'd switch out the cart for metal shelving 4-6' high x 12'' deep x 5-6' wide. The frames would have to move but it would get about everything off the counters and make the isle wider. Then I'd throw down a much bigger rug and look into those stickers they have for backsplashes.

As mentioned by others, looks like your friend needs more storage to keep the kitchen tidy and orderly. I would suggest a tall metal shelving offering more storage. Can't tell if the cabinets and appliances are white or off-white so in my suggestions for white she'd need to find a coordinating white to what's in the kitchen. Peel & stick tiles can be installed over the existing backsplash tiles, paint the walls in a warm white, and place a colourful runner along the counter. Here's the idea...

@lisedv The new image looks great.

The decor problem could be moot. If the landlord finds out that your friend is only using the apartment as a pied a terre, he will lose it. Rent controlled and rent stabilized apartments by law must be the person's primary residence.