Did either of you buy trip insurance? I'm assuming no.
If she cancels, she won't get too much back except taxes etc. If you don't get a roomie, maybe you can pay her the taxes and fees, leave her cruise fare in place and still be able to go with her as a no show. If you cancel (without insurance) you will lose the bulk of your fare too. Going solo is better than not going and losing all your money.
What is the dollar amount for the fare you are speaking of?