I would go shopping for a shower curtain that has pink and yellow in it. I would leave the area above the towel bar empty. I would remove anything from the sink surround that you don't need and place one pink/yellow/both liquid soap dispenser there.

If the plant is real, I would re-pot it in a pot that is pink or yellow or both. Pink or yellow towels - or a layered combo of them plus a tub mat.

Thanks for the input! I've been trying to find a shower curtain that was pink and yellow for the past few weeks, but I only found 2 that had yellow in them as a primary color at all. I couldn't even find fabric to have one made with.

Unless you want to go pastels, I would keep the yellow shower curtain. I would remove the towel bar on the lone wall. I would put the towel rack on that wall, a little lower than you have it now. In place of the towel rack over the toilet I would put two framed prints, the frames picking up the color of the wood tones of your sink cabinet. The prints could be florals, landscapes, even modern art but should have the yellow and pink tones you want. They should measure about 20x20 each and place one over the other.

The sink in on the far right therefore anyone washing her hands should be able to dry them there - place a hand towel holder on the wall next to the sink to the right of the mirror.

Place a tall plant ficus/palm, or so, on the left side of the sink to break the mirror from the pictures. The planter can be in yellow of your shower curtain, or pink or combo.

Hope you like my suggestios.

You're looking for hot pink and bright yellow?

Here is a link that might be useful: where to buy

This site has every type of shower curtain and fast delivery.
Is there any chance you could paint the sink vanity white? It would all look so crisp. Try and get the shower curtain in a fabric that has texture and then add more texture with your towels, maybe a small rug and wall art.
http://www.shower-curtains.org/showercurtainssitemap.html