Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
If there had been SAAver award availability for the OP's desired flight, and if she had Internet access, she might have been able to just book a new award ticket on ba.com for additional Avios. (But I'm not sure if BA allows for same-day award redemptions.) However, if SAAver seats were not available, her choice would have been to pay the going rate for a ticket or stay in Houston. That's just the harsh reality of last-minute travel.