Wow you are very fortunate to have received such a good financial aid package. You did not say if you had asked if the financial aid office if they could offer you even a little more, given that your sisters financial situation has changed since you filed the forms. Seems like a good idea to ask. I think you should jump on this opportunity to attend the U of R rather than deferring a year.
In the summer after freshman year many students stick around the area and work. You can find a room in a house to share with other students and live relatively frugally.
Also most students are concerned about the workload and the difficulty of doing well in classes when they first start out because it is a new challenge. Give yourself a chance to meet your challenges as you are probably well prepared if the school has admitted with the aid you need.
Go for it and buy yourself a warm coat (from Goodwill) when you get there.