Dr. Clark helped many people get well, but she couldn't help herself. Her first symptom was excruciating pain in her arms. Pain medicines were ineffective. It would turn out she had deterioration in her neck vertebrae which was pinching those nerves. Her hands stopped functioning. It would turn out later she had carpal tunnel syndrome. So as soon as Dr. Clark knew there was something wrong, she physically could not use her Syncrometer techniques to investigate it because her hands and arms did not work well enough. Her health deterioration was a mystery.
Well, not really. The cause of her health deterioration, while perhaps a mystery initially, is quite clear now. She had multiple myeloma. It's also a pretty lame excuse. I mean, come on! Clark "trained" dozens of acolytes to use her Syncrometer. Are they really saying that not a single one of them could use her device, which she claimed as part of the "cure for all cancers," to cure her cancer, as she claimed she could cure all cancers? Not that it would have done any more good for Clark than it did for any of the cancer patients who misplaced their faith by putting it in her, but the excuse used to explain why Clark died of cancer when she had spent so many years claiming that she could cure it is lame in the extreme. Surely there must have been someone who could have operated the Syncronometer for her!