Sorry about your Aunt. I think in this instance, you had a chance to change your outbound date and pay the fare diff plus change fee; that's about your only option.

Of course, it might not hurt to call back and try another agent. The worst they can say is no again.

In situations like this, the combination of very sick Aunt with rapidly changing conditions, and Priceline/award tickets with stiff penalties and restrictions, just doesn't mix well.