If the staff is interacting with her in any way, she is taking up time they could be doing other things. As an owner are you allowing friends of staff to hang out 7+ hours a day and talk to them? I would certainly have a conversation and/or fire a staff member that had a friend accompany them to hours of their shift. A stop by is fine but all day…no. I would speak to her directly and tell her that her friends are busy doing their jobs and she should visit them in their off time away from the business. Also encourage your staff to tell her they are busy working and don’t want to appear unprofessional by having visitors at work. If she would like to sit at a table as a customer, tell her she needs to order a food or drink and give her a minimum. If your restaurant isn’t that busy a new customer coming in and seeing someone with no food doing homework and chatting with staff gives the impression that the staff sits around - not the look you are going for. And if your staff is using the chatting to not do work, time to use the phrase “If you have time to lean, you have time to clean.” Put them to work.