It is incredibly frustrating when the kids have partially flown the nest and encounter difficulties - the instinct is to be protective, wrap your arms around them, and fix things for them.
However, @Nmeshed has a point. Looking at this from the perspective of all parties concerned, your daughter and her friends were initially aggrieved as their friend had scuppered their living arrangements, which may have coloured their interactions with the new girl. Similarly, this new girl may well have led a sheltered life and may not have had much immersion into wider British culture and perhaps sees new experiences as challenges as opposed to opportunities, and perhaps - yes - it's all getting a little much for her and her mental health is suffering.
She may well not have liked the suggestion of an interrogation council by your daughter and friends pre-moving in. Just as your daughter was let down at the last minute for living arrangements, so may she have been - hence why she was looking for accommodation at the last minute. That in itself is not a reason to judge her. And the fact that she may be of a lower socio-economic class than your daughter and have financing issues leading to university fees not being paid is most certainly not a reason to criticise her - I would hope.
You've mentioned that the day she locked your daughter out for 60 minutes, your daughter and housemates were accompanied by several others - amongst them large physically imposing males - in a group totalling 7 people. 7 vs 1? "Strapping" males vs one female? That sounds more like a lone woman sheltering in place, or indeed someone showing defiance in the face of conflict. The fact that she has told her father about the issues in the house, and that he is checking in on how she is coping in weekly phone calls also suggests that her perception may be that she is being intimidated by your daughter and friends - yes, it may be passive aggressive due to your daughter and friends being of a higher social class, but this girl appears to be able to read between the lines.
Without being there, you can't judge whether all is as your daughter presents it - and what has been presented sounds irksome but doesn't sound to rise to the level of criminality, as some PP have stated.
Go down and see how this girl is for yourself. If she truly is a threat to your daughter's safety, take your observations to the relevant authorities. But if it is just a case of people who have been forced together not getting on, help your daughter to build the life skills and resilience to coexist and deal with various people, as not all people in this life will like you or behave in ways that you desire or have a similar background to you. And if your daughter is to have a career in healthcare, this will be a valuable skill to develop.
This is all very unpleasant for all parties. I had some interesting housemates at uni myself, however, I feel stronger having grown through the experience and have drawn on those skills in my career over the years.
I hope that the issues are resolved and that your daughter can finish out the final 3 months of term pleasantly and productively.