If the station knew, or should have known, that the stunt could lead to injury or death, then yes, in my opnion they are liable.
I belong to a canoeing association where I have volunteered to lead trips; every paddler signs a release. Yet it is tradition in this group for the leader to evaluate each paddler and not allow paddlers to join the group if their inexperience or medical conditions could lead to injury or death. As a leader with knowledge of what is required I believe it would be negligent to allow an unsafe paddler to join just because they signed a release.
I guess it boils down to whether or not you believe that we are our brother's keeper?
But the hosts twice gave the woman an opportunity to get out of the contest by offering her tickets to some concert- she refused the first time and accepted the second- but even then suggested she could still go on if they helped her.