Just curious, because I know a lot of girls that do this and I do it at least once a week myself. Basically just leggings and a plain or unisex tshirt.
Most Helpful Guy
Yay a girl in class not wearing micro shorts and a low crop tshirt.
I would think that she is more there for herself than for a date. Those look like comfy clothes which usually mean that she is relaxed and wants as little stress as possible. She also might possible be on her period and is wearing that to be comfy.
I also usually give her props for being modest. With women around here that is a lost Character trait.
If I like her I would probably ask her out on a good day when she was wearing that. Or her normal clothes if she only wore that once or twice a month.1