Definitely highlight any leadership experiences you've had at the UofA. The biggest advice I can give to stand out is to talk to as many people as you can at Meet the Firms. You are more likely to get an internship if they know and remember who you when they look at your application.
The 3 primary qualities/experiences an interviewer looks for is to have strong skills in the following areas: Leadership - have experience being a leader in either a project, club, or group. Once you reach the role of a senior in audit (2-3 years depending on the Big 4 firm), you will be mentoring staff and leading the audit engagement. Teamwork - have experiences working in teams. This is essential for our job as you will always be working in teams on every engagement. Communication - ability to hold a conversation with someone and articulate your points clearly. This is important for internal (EY) and external communications (the client) on your engagement.