That's the incubation stage, when no symptoms are shown.

An infected person usually dies within three months to two years after the first terminal stage symptoms, often because of pneumonia or infection.

How long has she been doing this weird laughing/spasming/etc. shit? If it only started around two years ago, there's a definite chance that she has kuru. It also may be worth mentioning that she's powerful enough to have access to any type of medicine she wants- she might be staving off the disease somehow, although from what I've read about prions, that shouldn't be possible, but if she is doing that using some sort of experimental treatment or something, it will not keep her alive forever. Prions are nasty things to be killed by.

Edit: Another question to ask: If she knows she has kuru, why the hell did she run for President? She wouldn't have made it through her term, although, as I said, I guess it's possible she's using some sort of weird experimental treatment and figured it could carry her through at least to 2020.