Water is a good symbol to represent relaxation; The sound of the flows, rain, purifying and refreshing effects are all things that brings a lot of positive relaxing feelings.
Then for beauty, I think the hair of a woman are also an easy symbol often associated with beauty.
So what I could see is a mix of these 2 symbols together (see file attached, just a draft of copy/paste graphics from the web, nothing original). I'm just not sure this is really a symbol since it's 2 symbols combined together. And if you're looking to create an icon, it may not look very clear at a small size.
Another path you may want to explore is the Zen style and the soft rocks that are often used in spa salon as well.
The way they are relaxing is because of how it automatically reminds people about the "zen culture" but also maybe remind some people about the spa treatments using these rocks. The shape can also bring to mind the water and wind that soften them.
For the beauty part, these rocks have an interesting symmetry that is pleasing to look at and they are also often piled up in a way that I personally find full of beauty. Probably it's its simplicity that makes it so interesting in fact.
These rocks could be easier to recognize than my previous suggestion if made into a graphic for an icon. The sample attached might not be perfectly good for an icon but there are tons of nice pictures online that you may find better for this use.
I hope this helps!