Good to hear your niece is ok!
As far as firearms on military bases (stateside), DoD directive 5210.56, which was issued on February 25, 1992 authorizes DOD personnel "to carry firearms while engaged in law enforcement or security duties, protecting personnel, vital Government assets, or guarding prisoners".
If you wish to bring a firearm on base, you are
required to register the weapon with the MPs at the gate and follow rules that are similiar to many state laws. The rules that apply are:
Concealed carry is not allowed.
All firearms are CASED and UNLOADED.
A cased firearm must not be readily accessible in the vehicle.
Ammo must be as far away from a cased firearm as possible; ammo should be cased, if practicable, and not readily accessible.
All magazines must be unloaded.
And the followed is expressly forbidden:
Explosive Weapons
Machine Guns
Short Barrelled Firearms
Firearm Silencer
Switchblade Knives
Knuckles (brass/steel)
Armor Piercing Ammunition
Chemical Dispensing Devices
Zip Guns
Clubs or Night Sticks
Illegal Knives
I don't have the DoD link handy covering all rhe rules, but it should be fairly easy to find with a search. Basically, a military installation is no different than many other places in regards to firearms and common sense always applies: When in doubt, ask