I agree that she has the legal right to possess a firearm while on the premises and defend herself while on her drive , however, in terms of her job, it all depends on what her employee handbook says! My employer (whom I do not wish to mention by name) prohibits all employees, contractors and visitors (except LEOs) to possess a firearm or weapon of any type, on any company grounds (including parking lots) or while conducting company business elsewhere, regardless of whether you have a CPL or not, punishable up to and including termination of employment. Another stipulation in the handbook gives the company the right to search my person, my company locker, and my personal vehicle at any time, for any reason, with random surprise searches as well.
Legally, it would only constitute trespassing for carrying in a gun-free zone if you were to refuse to vacate the privately-owned premises. However, I am also legally bound to the rules listed in the employee handbook, which I was required to sign as verification that I have read, understand, and agree to all company policies. In order to gain employment with them, I have signed away my otherwise legal rights. Therefore, my employer would be fully within their rights to terminate anyone's employment at any time if they were to search their vehicle and find a legally concealed pistol (or other weapon, pocket knives over 3", pepper spray, etc.).
As other members have mentioned, it is up to you to put a value on your protection versus your job, based on the regulations set forth in the employee handbook, and that all it would take is a disgruntled coworker that has knowledge of your firearms and/or CPL to make a 'good faith' complaint to management that they have reason to believe that you may be carrying at work, possibly against policy.
