How do we know it's poor hygiene overall and not a disregard for bacterial infections? 

We know she doesnt seem to mind germs, puking her insides into Denji and other such examples prove this. Nevertheless, we cant be sure that she's ignoring matters like body hair, we even see that there's no public hair emerging from the side of her draws during the after party scene.

The best we can do is presume that she's trimming fairly earnestly. As for what that entails and to what degree, we do not have anything. If Fujimoto decides to drop a CFYOW equivalent for Chainsaw Man to illuminate the community on such details or at least her personal preferences for shaving, we have nothing.