Student professionalism

As nurses we are expected to act professionally in our interactions with staff, patients and families. Our profession depends upon that expectation for accreditation, integrity and trust. So, when you have a student who is already in their mid twenties, and should have some concept of professional behavior and an expectation of accountability, displays behaviors that are dismissive of those expectations, how do you turn that around. 1st incident: My group of 8 students left a conference room, with me in the lead, down one flight of stairs to an elevator 100 ft away to go upstairs to the assigned unit. I had previously showed the group where the elevator was and what floor we were on. We arrived at the elevator with one student missing. So as not to prevent the elevator from being used, we went up the elevator to the floor. I waited there for a few minutes while talking to the rest of the students, when some 20 minutes later the students arrived  with this explanation; "I heard that the oxygen was on and I went back down the hall to let the nurses know." "What?!" 2nd Incident: I told the students on orientation day that while they were expected to be at clinical at 0630, I gave them a 15 minute window till 0645 that if they could make it by then they would be allowed to stay. Citing the oft used "7 minute rule" in our area hospitals that gives the employee 7 minutes on either side of their scheduled shift time. My phone rang at 0430 but I don't answer that early. As  arrived at the hospital at 0600, I rang the number who had called me. The aforementioned student asked me if we were in clinical or simulation that day. As it was still early I thought for a moment about the sim day schedule and clinical and said , yes we are in clinical. The student said nothing else and hung up. At 0630, no student, 0645 no student, 0700 she shows up after assignments have been made and nurses have given report to the oncoming shift and students. I reminded her of the orientation conversation about arrival times and when I mentioned that she would be sent home, she went off! She became loud, threatening to sue me and the school, became belligerent to the point of me having to escort her outside, all the while stating that "it's the teachers responsibility to tell the student what the schedule is" and "don't mess with my education"! Well at this point it was either call the police or the school so I called the clinical coordinator. After discussing the situation with her, and letting her know that if I did send her home now there would definitely be a need for the police and that it was the first incident of being late, so I would allow her to stay. I ensured her that I would write up a student disciplinary form and follow the school's policy. Later I found out, that this may be a pattern and to make sure that I documented everything. The student returned to the floor and completed her day without incident. 3rd incident: We were about the leave the floor for post-conference and I told the aforementioned student to got to the breakroom and wait till everyone arrived and we would go to the conference together. Once I gathered everyone else and they were all waiting at the elevator, except for her, I walked the unit again looking for her, to no avail. I returned to the elevator and we went to the assigned post conference area. Thirty minutes later I get a call from her asking "where are we?", saying that she had went to the assigned area and we were not there. By the time she got to the room we were about done and frankly I was frustrated and tired of the situation. I dismissed the other students and asked her what happened. "I went to the assigned area and no one was there" she said. In her defense the assigned area she went to was about 50 ft away from where we were at the nurses station which she may have not seen us but would have been able to hear us. She thought that she could remain on the unit with out supervision and "hung around" till someone showed up. I am failing her at mid term for paperwork and behavior and would like to be completely rid of her but will need to follow policy. Please tell me what I did wrong and how to ensure that the student gets the education she deserves and I get the respect I deserve without turning this into a nightmare related to the "me too" culture.