How did she illegally take a weapon on a military base?
It's a common misconception that personal firearms are not allowed on military bases. I do it all the time, at Camp Bullis where I regularly shoot. They also sell firearms at numerous base exchanges, Randolph recently installed a gun counter.
Title 18 Section 930 of the US Code only prohibits firearms in Federal facilities, defined as buildings. It does not prohibit personal firearms on installations. Most bases that prohibit it are because of regulations (US Army) or commander policy (USAF_. I'm not sure what the Navy rules are as I haven't been on a Navy base with a firearm.