I thought there was another student with her but even then it is hard if they don't get on well. Do they have any halls of residence or could she move to a flat share with others on same course ? Is there a mentor at the college she could speak to ? iirc she has also been poorly recently which won't help , perhaps almost giving her permission to feel like this, everyone does from time to time, and a pamper parcel would help.
A lot of my DDs friends go home at weekends and they are Uni age not the age of your daughter. If she is lonely and the major problem is weekends then I would allow her to come home to be honest. You don't want her giving up a course that is right for her nor getting really down.
Volunteering might be more midweek stuff and that won't stop her rattling around in her flat at weekends.
My DD is happy on her own but she is 18 and she is also real loner type, so she enjoys the peace of it and always has stuff to do because that is how she has always been from a very young age. I expect, given her interests, that your daughter is far more sociable than that and, for her, being on her own is probably quite the opposite.