Well, Haru is only living true to her instincts: she's fast to sex because numbers mean survival of the species...
The antropomorphism applied to the story then creates all kind of paradoxes, choices and contradiction that should increase the fun.
I think Haru feels just a little too mature in how she copes with those harlequins brats and how she's able to cope with her most primitive fear instincts.

Minor detail from a precious question of mine about animal products: it seems normal to sell anything of value your body creates as they sell their winter fur as it sheds come spring. I guess it also works for eggs and milk.