It may be a legal issue. Check your state DMV code for guidance. In VA. the code states:
§ 46.2-1242. Parking in spaces reserved for persons with disabilities; local ordinances; penalty.
A. No vehicles other than those displaying disabled parking license plates, organizational removable windshield placards, permanent removable windshield placards, or temporary removable windshield placards issued under § 46.2-1241, or DV disabled parking license plates issued under subsection B of § 46.2-739, shall be parked in any parking spaces reserved for persons with disabilities.
1. No person without a disability that limits or impairs his ability to walk shall park a vehicle with disabled parking license plates, organizational removable windshield placards, permanent removable windshield placards, temporary removable windshield placards, or DV disabled parking license plates issued under subsection B of § 46.2-739 in a parking space reserved for persons with disabilities that limit or impair their ability to walk except when transporting a disabled person in the vehicle.
Perhaps the employee is not aware that there are legal requirements that affect her when the disabled person is not in the vehicle. In fact there are some places that even if you have a disabled person and disabled tags, once you have discharged the person from the vehicle you must not park in a disabled spot. The driver may not be disabled so vehicle access to a disabled spot is not neccessary.
Anyway I would have a frank talk, pleasent, but frank and inform her of any state law governing disabled parking AND relay the expectation of the company and the president. Should not be a biggie. 