What can she do:
Keep plugging a way at getting a part time job. Christmas retail will start recruiting in October. Pubs and restaurants take on extra staff for the Xmas period - look at staffing agencies. It's only a temporary job, of course, but will then show other employers that she has some experience.
The university will also employ students in the bars, cafes, helping with events etc- get her to start looking asap at their jobs portal. It's a smaller pool of applicants than jobs outside uni
Volunteer but do it strategically - if she is interested in educational or health and social related psychology, then volunteering as a mentor for teenagers or people with certain health conditions would be very useful in future applications. The university will almost certainly have a volunteer co-ordinator/info pack and may run their own schemes like widening participation where they go into schools or work with people disengaged from education. Also look at any youth groups or groups working with people with mental health problems as they often have befriending or mentoring volunteering.
This will help a lot with future job applications.
Summer jobs: again, be strategic. She wants to earn money but also show useful experience ideally plus maturity, ability to deal with challenges. Look at jobs working in holiday camps for children including specialist ones offering respite or hosting families with children with special needs. Look now at old job adverts - how can she be a good applicant? There may be opportunities with the university to complete a first aid course for example - student unions often have a St Johns Ambulance group who do. Check both universities in your city. It then ticks a box for summer job applications next year. Uni volunteering will often mean she gets a DBS disclosure done so again, great to have that in place before summer job applications.
First aid and DBS also opens the door for babysitting and nannying - summer nannying is a potential job while also showing working with kids. Look at Koru Kids for example.
Extra curriculars: look at the student union groups, join something interesting, help run it and have a position on the management group for it. Doesn't matter if it's netball or knitting, it shows the right social skills.
If there is a psychology group, join it. Go to their talks, be on the board, suggest events, meet the speakers who come. It shows real interest in the subject beyond just the classes. Lots of students show very little interest in their subject beyond the minimum so stand out.