Is this a detail that I should include or not?

It doesn't creep me out at all. If it's part of the story, Lily, then put it in! I know my favourite author writes series in the world of Tortall, and each of her female heros always go through getting their cycle for the first time and they have to go out and get a protective charm for it. It's part of the story, so it needs to be in. If you feel its important, put it in Lils :}