Guin: On the sink/counter, there will be a bottle of liquid soap and a hand towel hanging on the rack. Then, on the shelf on the opposite wall, she’ll have a jar with seashells, and a basket with some frilly towels and some fancy soap.
Is that okay?
Sorry, not really. True thoughtfulness is not expressed by decorating your bathroom with soap and towels that look like soap and towels, that are constructed of the same materials as soap and towels, and that are physically accessible like soap and towels—and then expecting your guests not to use them as soap and towels.
Even if the “real” soap and towels look more accessible and more useful, as you describe them, it’s still fairly easy for someone to mistake the fancy stuff for actual soap and towels. Especially since, as many posters here have noted, a lot of other people’s bathrooms have fancy soap and towels that are actually meant to be used.
Another aspect of this practice that makes it contrary to etiquette, although this is getting kind of subtle, is the “too good for you” connotation. Gracious hospitality is supposed to imply that the members of the household are eagerly providing the best they have for the enjoyment of their honored guests. Reserving better-quality things for the use of the residents and offering guests only the second best is an inhospitable rudeness. (Of course, the good stuff that you hide away out of sight doesn’t count!) Polite people may never suggest that the things they enjoy are too good for their guests.
Decorative soaps and towels that are obviously finer and fancier than the usable ones seem to insinuate “The fancy stuff’s too good for you, use the ordinary ones.” Yes, I know that the residents aren’t actually daring to use the fancy soap and towels either, but they still carry that unpleasant “too good for you, don’t touch” aura. They hint of cheap, pretentious hosts who want to have the appearance of graciousness by offering elegant things for the use of their guests, but don’t want to incur the trouble and expense of having to clean or replace them when the guests actually use them.
Yes yes, I’m sure your mom’s not at all like that sort of person. So why would she want to follow a silly custom that subtly hints that she is? As the OP suggests, if you just want to make your bathroom look pretty, why not just put some pretty stuff in it that isn’t soap and towels? Then nobody will be confused or feel subtly disparaged, and they’ll probably enjoy looking at the pretty stuff too.