She may be home for a month at Christmas and at Easter (we go away on holiday for one of those) and back in June for the summer. But 30 ish weeks of the year her room will be empty and her sister crammed into a box room. If the rooms were more evenly sized it wouldn't be an issue. If she chooses to stay longer than just the term weeks (her let is 38 weeks), to work or just to enjoy living away from home, it will be less time that she comes back for.
Above all that, we should have swapped their rooms years ago. DD1's extremely minimalistic and has practically nothing in her room. For many years DD2 had the big toys etc and should probably have been allowed the larger room. But we did the eldest-has-the-biggest-room. She will be used to a smaller room in her digs so can have the smaller room here too. I will make sure it's decorated in her style.
Will your DC be looking for work in their Uni town, or relying on holiday work? DD has already been asked by her pt casual job she got in June whether she's coming back at Christmas. I hope she'll pick up a few hours somewhere as it gives her something else to do as well as her studies and another chance to come out of herself a bit and meet more people, as well as the obvious bonus of work experience and a wage. Are student jobs easy to find when they are then home away from their uni town for a month at Christmas and Easter?