I've been avoiding commenting on this. I have an ex-girlfriend that was a Scientologist, so I know way more about it than I care to. People seem to like Kirstie Alley, so haven't wanted to spoil what might have been an otherwise feel-good thread.
In any case, as she was a Scientologist, it's almost certain that she was doing the "Purification Rundown" to help treat her cancer.
en.wikipedia.org
Which, basically, is a sauna and a regimen of B vitamins.