Like Dee, the Waitress (her name is never given) started as basically human. Each time she shows up, though, we see that she isn’t as together as we initially thought and as she would like to project. She is also like Dee in that we get the distinct impression that she views herself as someone adventurous and philosophical (traits associated with the Sagittarius sign), but she’s really just a barely functioning adult who can’t keep a job.
Most people would probably say that they dislike “clingy” people, but since this is specifically listed as one of Sagittarius’ dislikes, it makes sense to assume that the Waitress is the best example of the sign the show has. For her first few appearances, it’s made crystal clear that Charlie is stalking her. She issues restraining orders, but nothing seems to help. That was her defining characteristic until we learned more about her.
One way in which we see her Sagittariun idealism is in her crush on Dennis. Of course, Dennis has no real feelings for the Waitress, but enjoys leading her on. Obviously, she should be well aware of his reputation and manipulative tactics, but she can’t get over the fact that she wants to be with him. Even when she makes it clear that the way he treats her is damaging, there’s still a part of her that hopes he will finally change and be with her.