I am a mentor not a student, but if this was my student I would be contacting the university immediately and expressing deep concerns. Support from the university tutor is a must when things are not going well. You will need to show you have involved them at all points and taken their advice. It is also nice for you to have their support because failing (or even nearly failing) a student is a really horrible thing to have to do. I think you need to act tomorrow and not keep leaving it. You don't say how long the placement is, but if this is the situation after a few weeks, it isn't likely to get better. Sod sensitive, you have probably been 'nice' and 'sensitive' and 'tactful' til you are blue in the face. You need to get a bit tough with them and be blunt about the fact they are going to fail this placement if they don't shape up. Good luck.