How to deal with a student lacking commitment My question is whether anyone has advice for dealing with difficult students. Specifically, if a student is taking up your time/mental energy and you can no longer justify this investment, how do you distance yourself while still remaining supportive?

Apologies in advance for the length of this question.

I am a PhD student currently supervising an undergraduate student completing a short lab project as part of their bachelors degree in a lab where the main supervisor has been unavoidably absent recently. In addition to this we are a small lab with broad research interests, as such I am currently the only lab member apart from my supervisor who is qualified to oversee the project designed for the student.

I have found the undergraduate student very difficult to work with, a fact I brought up with my supervisor quite early on. My supervisor asked me at that time if I would be willing to continue with the student. I was optimistic and believed that I could reason with the student about their difficult behaviour but that now seems to be off the table.

Their behaviour is surprising to me and I have a difficult time resolving it as it seems quite bizarre. I have had several 'talks' with the student now regarding their behaviour which includes a range of single incidences that caused problems in the lab. Additionally the student does not handle unforeseen situations very well and so, I have been supervising them closely at times, which costs me time and has resulted in me working later and on weekends. Finally, the student has, despite assurances to the contrary, made it clear by their actions that their priorities lie elsewhere. This final point is perhaps the one I find most bizarre as this project is 4 months out of a 4 year degree but will affect the final grade significantly.

I feel that I have been open and  honest with the student, I have given them a chance to address behaviours which may not be suitable (I had assumed that they may not understand that they were now in a place of work, not a teaching lab). I have also informed the student that if they feel I am being too cold or they need a break from work to let me know - as the student often seems to become quite visibly stressed - and I could try to accommodate this. Overall I don't feel there is anything more I can do.

I have recently been informed that they have messaged my supervisor implying that my apparent 'harsh' behaviour is the reason for their lack of progress. This doesn't worry me as I have a good relationship with my supervisor and have supervised students before without issue - though never as closely as this. 

At this point I feel I should cease close supervision of the student and my supervisor agrees. However, I worry that left alone the student will not be able to deliver a good project and will attempt to justify this - citing for example a 'sudden' lack of supervision. I am also reluctant to leave the student alone to perform large experiments required to finish the project as they have previously shown themselves to react quite badly in stressful situations. 

In summary I feel between a rock and a hard place, do I continue to guide the student and possibly suffer the 'consequences' of their apparent belief that their slow progress is a result of my supervision and not their lack of commitment. Or do I leave the student to their own devices and risk them failing - a very real possibility from what I have observed and something I wish to avoid as it is a good project and I want the student to do well.
First of all, people are not mind readers; so first tell the student that he/she needs to work harder. and then: 

Longer Time Intervals: This worked for me for number of students. Basically double the time intervals between meetings. So for example, if you meet the student every week, tell him/her that his/her progress is not satisfactory so meet me in two weeks time and tell me what you did.

Warning With a Help of a Senior: Then give a warning for the next time interval, and tell the student if he/she keep working like this, you will not support him/her anymore. For this, it is better to have a senior lecturer (e.g., head of a group) in the meeting as well. 

Refuse of Support With a Help of a Senior: Then, if the student progress is not satisfactory, have another meeting with the student and with the help of a senior lecturer let the student know that you did you best and because of the student's lack of progress you are not willing to work with him/her anymore. So, he student needs to find another supervisor to work with him/her.