She worked in the armory, so she’d have no problem with someone allowing her in. I think she changed into PT clothes, and went outside with every intention of returning.
I am skeptical of the location of the phone ping, as that post was deleted. The charge on her card is also a rumor, and hasn’t been repeated by either CID or her sister (as far as I know).
That’s why I think they are searching for her on base.
She would still have an NCO who has the keys to open it for her which would have still been a hassle for both of them.
From what I’ve read, she was wearing purple leggings and black shirt which is not the PT uniform.