I would think a shoulder holster would work, or perhaps something mounted to her chair.
If she is well endowed, perhaps a 'Flash Bang Bra' would work. Depending on how big of a gun she is concealing and how much coverage she has to conceal it, some gals find these things actually work. I guess the support system is there already, but I just can't fathom having a gun poking me in the chest all day long.... Maybe it's really not as bad as I think.
Here's one review, there are many!
Flashbang Bra Holster Review | Shall Not Be Questioned