Is it rude to ask an unaffiliated student to leave the PhD student office? I work in an office space shared by 3 professors. We have bullpen style desks and around 75% of them are full. The lab is somewhat spacious.

One of the first-year PhD students (not my advisor's student) brings in her friend with her to the lab everyday. They hang out mostly, often taking naps and such. The friend uses the lab microwave and has lunch in the lab everyday. They are generally very quiet and not disruptive. The friend is not a PhD student and as such not a member of the lab.

Would it be rude to ask this person to not come to the lab? I've spoken to the rest of the people in the office and they don't care at all, but it bothers me that they are treating the lab as their living room (given that they are here from 10 AM to 8 PM, most of it involves sleeping or using their mobile phone). What would be the right thing to do here? Do I just ignore them or do I ask the person to leave given that they are not doing, nor will ever do research for any of the 3 professors.

Has anyone faced a similar situation before?
I will mention that while Nicole Hamilton's answer is fundamentally correct—this is an issue for your advisor, as well as the other PI's in charge of the office space, not you—there is one issue worth elaborating on.

In particular, it is an issue if someone who isn't part of the department is using the department's facilities, because of the liability issue if something were to happen. For those grounds, it would be especially helpful to mention that one of the people coming into the space is not actually authorized to be there at all.