This is a natural occurrence, and it is one of the realities of the body with which women have to deal.

If a woman is comfortable with one, a tampon is the simplest method of dealing with that time of month. If an external conveyance is preferred, then she would wear shorts or bikini bottoms.

For the most part, a woman should use what she feels is less obtrusive for her personally; others aren't going to notice or object.

from rec.nude

Not all Danish naturist campsites will allow you to dress partially or "sexy". Somewhere a small bikini bottom might be considered sexy, and you will be asked to cover up (or dress down).