My impression of Tai has always been that she takes individual things seriously or not based on what is important to her, not based on social norms or expectations. For the purposes of the job, that means that all of the work gets done, students are given needed help, etc., but she doesn't bother with dress codes or other elements of traditional formality. I don't see her as someone who would get high at work often, if at all.
This is, for example, why she was willing to hire Marten immediately and has kept him on. If she were high all of the time he likely wouldn't have remained working there for long, either by his choice or her randomly changing her mind. Instead, she hired him because she had a good feeling about him as a person, which has been borne out by his willingness to learn and do the job rather than to simply coast. She did not worry about his experience or long-term ambitions, because neither affects her view of the world.
Working on this assumption, I think that the "good job" review is basically a joke. She may ask the interns to write their own evaluations, or to write them for each other, but she has probably already written real ones and would use that exercise as a test.