You may want to post on the financial aid forum...
Do you already have the full Stafford loan for a freshman in your aid package ($5500)?
If your mother applies for a Parent Plus Loan and is denied you will be able to take out additional federal loan money in your name for about $4000 for the year without a co-signer.
Banks will generally not loan 18 year olds money without a co-signer, so a co-signer will likely be needed for additional loan money.
What are the direct billable costs at the school? How much are you paying in rent each month, how much do you have in your budget for books, travel, food, etc.... You may be able to cut expenses a bit. Do you have a summer job? Can you try to earn more at that job? Will you have time to work during the school year?
How big is the gap you are trying to fill?