Hillary hates campaigning.
For candidates who love it (Reagan, Bill Clinton) it can be invigorating. But someone who hates it, who has an entitlement mentality about the job, it can cause all sorts of mental and physical problems.
Look at George HW Bush in 1992, disinterested in campaigning, suffering from Graves Disease and probably overmedicated.
I give it better than even odds that Hillary wears down very quickly during the campaign. All it takes is one trip, one episode of slurred speech and she’s going to be in deep trouble. If only from he fact that she’ll need to then overcompensate to prove the incident was a fluke, which will wear her down even more.