Will her condition affect her ability to physically or mentally perform the job? Note that the physical side of things, aside from stamina for long hours and limited sleep, is pretty minimal. If not, then who cares?
Will her condition significantly increase the likelihood of her dying in office? Makes the vice-presidential nominee worthy of a lot more scrutiny if so, otherwise who cares?
Presidential health has not always been much of a limiting factor. Interestingly enough FDR, who had been crippled by polio and would die in office of a stroke resulting from congestive heart failure, didn't make their list of 10 unhealthiest presidents...