The gag here is that it's either confiscated whenever she takes it out, or it's out of ammo anyway so it's useless. Maya took Celeste's gun the minute she took it out in Chapter 4. Chifuyu, Ichika, Laura herself do it as well. She complains that none of the other kids get her treatment, but Ichika points out that none of them are carrying lethal weaponry and some can't even be considered weapons (Smiles and Books
)
At what age do ids tend to notice innuendo's and stuff like that?