OP - I had a tough first year. I had had a sheltered upbringing, little in common with other students and poor social skills. Learning how to make small talk and find points of connection with just about anyone was a huge discovery and made a big difference. I never really gelled with the very privileged London types - we just had too little in common - but the student and city communities are large and diverse. I trusted that I would find my niche (as all the welfare guides said) and it did eventually happen, one connection at a time.
I do remember not having much work in the first year, and often being bored while others were working during the day. It took a while to get involved in societies and projects, and then I was suddenly too busy. If she is finding that she has too much free time, then she needs to find a way to fill her time. It may also be that others simply need less stimulation, and she needs more. It doesn't mean that the others are dull, just that she has particular needs, but it's a very solvable problem.
You don't have to be super-fit or committed to join one of the more relaxed rowing teams - she should sign up next October. There is nothing like messing around on the water on a spring morning. I didn't row in my first year, but tried again in my second year, made a lifelong friend through it, and carried on after I graduated. If not rowing, exercise helps more generally - sports like boxing or roller derby are very sociable.
Having a project like visiting every college/college chapel, every tower, every museum/historic landmark - ticking them off would help build a stock of memories. There is so much to see, and very soon it will be time to leave - she is already a year down!
So many of my peers never went to the Cowley Road, or Godstow, or out to the Cotswold villages. Walks along the rivers and canal were really lovely. There will be a walking club which is very low-cost and gets people out of town.
Many local charities would be thrilled to have her helping out - washing dishes, leafletting.
There are many good small music venues, lots of concerts, lots of talks. The various arts festivals will often have roles for volunteers so that they can see things for free in return for helping out.
She could work on a new language at the language centre, then find a student from that country to practice with. If she's attracted by studying elsewhere, Erasmus is opening up again to UK students next year, and some colleges/degree programmes have relationships with US universities too.
She needs to think of the value of a wide network - meeting more people, even if she doesn't get very close to most of them, means she's more likely to find the people she clicks with.
In my final year I realised that it would all soon end, so made a bigger effort to go to the additional lectures/seminar series. They were superb, and I felt so stupid to have not made the effort earlier. They don't have to be compulsory to be worthwhile - and also did help my performance in finals because I had more breadth and more proximity to graduate work. I remember very young PhD students giving talks who, years later, went on to be world-famous.
Many societies and the central students union really need capable people - you do have to put something in to get more out.
It might be useful for her to really think about what things really fascinate and motivate her - shared interests attract friendships. Does she have a sense of what she wants to do later on in life? What are the things that she really cares about? If she is clearer about who she herself is, her types are more likely to recognise her.