They may not own it but might they lease the car park? If so they have a perfect right to insist that people parking there obey their rules. They want as many customers able to get in as possible, and that's why they paint the lines so the spaces are just a little too small.

No one is entitled to a parking space at work - just ask the nurses. How about her employers or the car park owners just tell her NOT to park there at all - problem solved?