It would be fair to say this bid was doomed from the start. She is citing family health concerns as the reason for departing the race, but clearly this bid was the longest of long shots. If she thought the Cheney name was going to garner establishment support, she was wrong. In fact, what it brought was establishment scorn and a rally of support to the incumbent.
With two polls showing her trailing Enzi by wide margins, this departure isn't surprising, whatever the reason.